This is rather a difficult question to answer. I will try my best. Where do I start?
The situation as explained above reflects (usually) generation/age differences, not so much about what knowledge you personally have. Older generations/ages tend to say "Man, if I could be your age.." in spite because they know with the knowledge they have now and the youth you have, that person could ultimately make life altering changes. It's not jealously being questioned, but frankly, it's just a simple wish or wanting to be young again.
Anyone, even you, could say "If I was younger with the knowledge I hold now, I could be a better person." The statement is valid, however, it remains as a personal depiction of how you might better your life. However, when someone else wishes to be your age, simply take the phrase as a compliment.
I would not question them on what they want to know. The knowledge you hold may not be of interest to them and therefore could result as to why you couldn't get the answer you were seeking. At this point, what you seek becomes moot because people's interests, passion, ideas, creativity are relatively different.
Asking them what they would do at your age* would make them reflect about their current life situations. Even thinking about being a younger age is quite irrelevant. This is because, in all actuality, this notion will never happen. Ever. So why continue to think about it?
I'm hope this answer makes sense. Sometimes my explanations are flawed, and this probably is, but I hope you understand the gist of my words.
Certain threads on this forum remind us, and I will wholeheartedly never forget it, is to be just damn possible best you can be. No one could ever ask for more, no one ever will.