I think I know that feeling you're talking about, cherrytree. It's the one I got when the last of my 3 brothers passed on (all 3 died too early) and I realized I was the last one left of those who lived in my house growing up. Now and then, that feeling still comes over me. I'm not the oldest in my family - I have a few cousins older than me, both male and femaile. But as my parents and brothers are all gone, I'm the oldest one left from that household.
Most of the time, though, like yourself, I'm very happy. I take much joy in my DDs and my DGC.
Even if I were the oldest member/female in my extended family, I wouldn't worry about dispensing "pearls of wisdom" to the younger people. Not sure I have any, LOL! And they probably wouldn't want them, anyhow! My DDs and their friends, at least, seem to be more interested in seeking information on the Web than from any of us GPs or older cousins and so forth. LOL!