I don't know what I think about age.
I'm 11 years younger than my husband and 8 years older than most of my friends, who are mostly in university "the first time around" (whereas I'm on Round 2.) I'm 11 years older than my step-daughter. Those 3 years difference sure make a huge difference between her and my friends, or maybe it's just that I've "clicked" better with friends who are mature for their age.
One thing that always makes me laugh is when someone insists they are mature for their age. I've never met someone who claimed this for which it was actually true. One girl I met at Pride last year refused to tell me her age, insisting that it would change the way I thought of her. I'm bad at guessing age, so I didn't even try. She told me she was mature for her age. Meanwhile, the only reason she ever called me was to ask me to come drive her somewhere. Sure enough, she eventually told me she was only 16. I never figured out where the mature part was supposed to fit in, I never saw it.
My husband is dying to go back to college. He's quite honest about the reason: so many pretty young girls in tight jeans :P He likes to look at them, but he's no idiot. He knows that these girls are not remotely able to provide for him the things that I can: stability, someone who cleans up after herself and knows how to do laundry and even cooks once in a while.
I would never worry about being replaced by a younger model. We're not cars, and if we've married someone with half a brain, they'll know what they have. It's fun to have flings with younger women, and there may even be some love that develops, but I don't think it could ever replace something established, comfortable, timeless...
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker