It can mean "how old were you when you left home", but I don't think that there is a strong implication that that's what it means. As always, the context will make that clear. For example, I think it's typical to use "leave home" in police crime dramas, where a detective asks a person or people, "When did you leave home?"
I thought it was generated from recorded bits, and that the recorded bits are combined to form sentences. The only basis I have for that is that the individual bits sound to me like real people speaking. If the sounds were completely generated, would it have one voice (the female one) speaking with a South American pronunciation and another (the male) with what might be Mexican pronunciation?
I do not know any details, but it seems that both male and female voices (randomly) fluctuate between /j/ and /dʒ/ pronunciation for 'y' and 'll', and female voice has a greater (equivalent of natural) tendency to drop consonants at the end of words. None have (thankfully) the Spanish lisp.
I had to look up the IPA symbols. The whole thing of pronouncing "y" sounds as English "j" or "zh" is very common in South America, some countries more than others. My guess was that Duolingo had real people recording hundreds of words, one at a time, and that the "y" sound would vary a bit from word to word, as it can in actual speech.
I think I hear it more in the female voice. And I agree that she drops those final "s"s all the time. The one thing that I hadn't heard in a real speaker before was not clearly articulating unstressed vowel sounds in final syllables, so that when she says "ellos" and "estos", it sounds like "ellas" and "estas" to me.
In Spain, the plural you is vosotros (vosotros salís).
In Latin America, the plural you is ustedes (ustedes salieron). This form uses the 3rd person verb form, that's why it might be confusing (since Castillian Spanish (spoken in Spain) uses a special verb form.
So, ustedes salieron isn't they leave, but you (all) leave.
"Ustedes" is the plural of "usted" (see below for usage), and both are "you" in English (well, "ustedes" is "y'all" in the South, and there are some other interesting regional forms of plural "you" in English). So the translation should still be "you" (or probably "you all" is accepted).
In Spain, they use "vosotros" for the plural of "tú", and "ustedes" for the plural of "usted". But in Latin America, they don't bother with "vosotros"--instead, they use "ustedes" for both the plural of "usted" and the plural of "tú".
Also correct should be "when did you leave from home."
In English, there can be a slight difference between "leave home' and "leave from home."
"Leave home" can refer to "leaving home for good" as in "moving out." "Leave from home" can imply a temporary departure "leave home to go to school".
"Salieron" is really the form of the verb associated with "ellos" and "ellas". I believe the "ustedes" - "you" plural or "y'all" in American slang - is here to make sure we know we're not relating to "they", but rather to "you" plural, y"all. "Ustedes salisteis" is actually correct but apparently not popular/used. In English "you" is ambiguous and as you can see also problematic. Do you (and you all, y"all) agree with me?
In American English there's a huge difference between "I'm leaving home and not coming back" and "I'm leaving the house and I'll be back at six." In Spanish maybe "Yo salgo de casa..." and "Yo salgo de la casa.." ? In my opinion "go out from the house" and "when did you leave from home" are not correct. "When did you get out of the house?" is good.
To stress that difference I would probably say something stronger like ''me voy de casa'', ''me marcho de casa'' or ''dejo mi casa/mi hogar''. Anyway I don't think 'the article ''la'' would make such a difference, plus some regions in South America use ''la casa'' in the place of ''casa'' so that would be problematic... But that's just me. Maybe some native speakers will share
Yes, it's offered (but not really emphasized) later on. There are a bunch of exercises where the correct answer shown is in the "vosotros" form, but you can answer with any "you" you like, so it's possible to avoid using it. It will also be shown in Spanish sentences, so you will need to recognize it to be able to translate it as "you".
This is strictly personal preference, but I would not accept "y'all" — it is not formal English. I understand why some would prefer to see it here (singular/plural 'you' is problematic enough), I realize that numerous people use it in daily life, yet it is very regional. There is one more reason I am against it: it is often used as singular 'you'. I remember first reading about "y'all" on a tray mat in a Tex-mex restaurant in Boston where it stated that despite its obvious origin as an attempt to pluralize 'you', in modern Southern vernacular it is normal to address one person with a "y'all". Lo and behold, several months later in Texas someone did address me (I was alone) with a "y'all", just as the tray mat told me they might.
That could be because, as a roommate of mine once declared, "Texas is not the South--it's the Southwest!!" And there's also the chance that the "y'all" extended to a sense of "you and your family" or "you and yours", even if the others weren't there with you then.
I live in the real South (NC), and natives here are very confused if you say "y'all" and just mean one person (or if you say "you" and mean multiple people). It is not done, and I've lived here since 1975.
I am fine with Duolingo's accepting various regional forms of plural "you", because it's not here to represent only formal English. It doesn't want to discourage people by not accepting translations that reflect the way they actually speak. So as long as Duolingo accepts the correct formal usage as well, I don't care how many folksy regional variants it also accepts.
I would never deny your experience. But I am going to propose a couple reasons for that:
You actually did not hear it in all your time in Texas.
You did, but it is so normal, your brain did not register it, since there was nothing out of the ordinary for you.
I vividly remember the moment I described specifically because it was so jarring to hear something that I had both known about and (subconsciously, perhaps) never expected to hear.