To be honest 17 is very young. I'd employ neither, without something that blew me away. I don't know that making that comparison is really relevant.

30 years and no work history implies some problem that has prevented them from working.

17 years implies a lack of life experience and likely a lack of soft skills. Once they hit their 20's however they're going to be less of a gamble, regardless of their work experience.

So yes at some point too much time will have passed for them to become more employable. But I was only thinking in a sub 5 year term. More as a means of encouraging someone in that situation, not as a hard and fast rule, that the older you are the more easily you're employed.