You should read a textbook about historical linguistics. Actually one that I can recommend is called "A History of Languages" by Tore Janson (and there's an older book that I believe has some of the same material, called "Speak", I believe).

By "Jewish language" you probably mean Hebrew. It's old in the sense that it has been documented for toward 3 millennia, but it isn't the oldest documented language, or even the oldest continuously documented language. (That is probably Ancient Egyptian, which then became Coptic ans is recently extinct, or maybe still spoken by a handful of people. Sanskrit also has a very old history. Chinese is documented almost as long as Hebrew, I think. And then Akkadian and its modern descendants (now endangered) are almost as old as Egyptian.)

But what is an "old" language. That description actually makes no sense. All languages are old. Older than history. (There are a few that are "new", because they were born recently in some sense-- for example, pidgins and creoles, and some sign languages, but those are special cases.)

Languages change, spread into dialects, and then those dialects become hard for speakers to understand each other. And then we call them languages.

Importantly, speakers of (Modern) English today cannot understand Old English from 1000 years ago. Some languages have changed less (for example, Icelandic is almost the same as Old Norse and speakers can generally read old texts without too much trouble) but all languages change. Speakers of modern Hebrew cannot (fully) understand Biblical Hebrew without education. Of course most do study that older form of the language, so they can read it, but that's not because it's the same as the modern language.

Germanic is a family of languages that all descend from a common ancestor (known as Proto-Germanic, which is not directly documented). Both English and German are descendants from that. But English did not come from German itself. They're just related-- daughters of the same mother.

You can read more about this on Wikipedia easily:
https://en.wikipedia.org/wiki/Germanic_languages

And the Germanic languages are just one sub-family within the larger Indo-European family:
https://en.wikipedia.org/wiki/Indo-European_languages

I would very strongly recommend Janson's book (this is discussed mostly in chapter 2-- chapter 1 is about what a "language" even means).

For more about Proto-Indo-European and how those languages spread and where they came from, check out Anthony's (2007?) "The Horse, The Wheel, and Language".

As for a first language, we don't really know. Janson jokingly points out that based on current theories and evidence we can be fairly certain the first language was spoken between 40,000 and 2 million years ago. We don't know. But we do know it was at least tens of thousands of years ago: humans who migrated that early all share the same genetic ability to speak languages and probably inherited something from the same or similar early languages, maybe even a "Proto-World". (We can't prove or even really argue for a single Proto-World language, but it's an idea most linguists would probably expect to be correct unless we found some evidence against it.)

There has been a lot written about these topics, and almost all of it is very speculative. Beyond the couple books you're starting with, the next step would probably be to look at an overview volume that either compares theories or has contributions from different perspectives so you can start navigating for yourself which approaches you prefer.

Another place to start might be Berwick & Chomsky's recent book from this year, "Why Only Us?" -- it discusses the origin of language (mostly syntax) from the perspective of syntactic theory. I'm not mentioning it because I necessarily agree with it, but because it's new and getting some attention in the press. It is, like most other works, quite biased toward a particularly approach and based on certain assumptions. And then like other books it also takes a fairly dismissive approach to other theories, which is somewhat ironic in a field that is mostly speculation. I would only recommend this book if you're interested in syntactic theory or the contributions of linguistics to the question. But in that it's interesting, not that you need to agree with it.

Janson's book is really nice because it gives such a broad overview and doesn't attempt to make any arguments beyond what is obvious. The rest will end up inevitably choosing a direction, and, logically, most of them will be wrong.

No single "language gene" has been found, but a lot of people have searched for it! FOXP2 was reported a few years ago to be "the language gene", which was exaggerated in the first place and has been basically debunked by now, but it might interest you to read some about it. Note that Neanderthals might have had sign language, regardless of their anatomy. So even whether you're looking at bone structures or considering cognitive ability, you may bias the answers to whether Neanderthals "had language" or "could have had language". I don't know that there is much consensus at this point, but it's certainly possible they had language in one way or another. It is known that they interbred with modern humans some.

If that is the case then presumably there could be indirect evidence which could point the way to establish when the mechanics was there to allow for speech.

I guess speech is not the same as language, but I guess most people would agree they are close enough in humans.

Again, signed languages might predate spoken language, so that would be irrelevant. This might fall into the "we just can't know" category. Some people have even proposed that language probably originated as signed language, not spoken.

So with genes, bones et al, I think we should not be far from finding out when the first languages might have arisen.

The amount of speculation and lack of direct evidence is just so great, we are very far from having any kind of definitive answer. I think many researchers have felt like you did, but given that no one has found an answer is well over 100 years, that suggests at the very least that it's a hard problem to solve. Some journals have even banned discussion of the topic because the endless debates seemed pointless!

The missing part is establishing when symbolic thought arose. I expect that is why the 40k is suggested by Janson, given the first stirrings of cave art in Europe.

That's part of it. But the latest dating to about 40k years (or even earlier) is also due to an argument from Chomsky and others: any human baby can learn any human language (think about international adoption), and therefore we all have the same basic biology for doing so. So--

In that case I suppose it is reasonable to suppose that language was developed before modern humans came out of africa.

Right.

I recall there are discussions whether this was 80k or 120k or somewhere in between, but it would put the time farther back.

Janson's 40k is a bit narrow in my opinion, for the reason above. But all he's strongly claiming is that it isn't any later than 40k years.

No idea what to say about the 'experiment', except that hearing a "foreign" language would not be surprising in such a scenario.

A video I've shown my classes might be of interest to you. It's an episode of NOVA from about 20 years ago. I don't know if you can find it anywhere, but apparently there's a transcript here, along with information about the episode:
http://www.pbs.org/wgbh/nova/transcripts/2120glang.html

I heard that the Jewish language was the oldest in the world. Question, why are there so many languages in the world to start with? Is there a difference between the Jewish language and all languages today and how did English come from the German language? Linguistone 

This is a question that various people ask at various times, and that is why I take it up, too. The answer is given in the Hebrew Bible, almost in the same breath as the affirmation that all humans descend from .a first man (Adam). Both positions can be refuted empirically: By doing etymological investigations, it can be shown that Hittite, Canaanite, and the modern European languages cannot be traced back to Biblical Hebrew. (Rather, Hebrew had diverse sources.) As for humans, you need to know that racial traits (physiognomy, colour, etc,) are inherited, and that opposite traits could not have  belonged to the first human couple. So, the theory of the monogenesis of humans and of languages must be rejected.