It's sometimes so awkward.
I work with a guy 20 days younger than I am. On a few occasions when we've met with vendors or clients together, I've been the recipient of condescending comments regarding my youth while the older vendor/client guy groups himself with my slightly younger co-worker as the older/wiser/more experienced superiors.
I never say anything because I don't want to embarrass my coworker.

A lot of people in my ward don't know that I have adult children. When they learn that I have grandchildren, they sometimes seem nearly offended. "Your not old enough to be HIS dad" or "How can you have grandchildren at your age?"

People have told me to my face that they guessed I became a father when I was in highschool. The reality is that I was 2 months shy of 26 when my first was born. I was a returned missionary and a college graduate first.

I'm sure there are advantages.

I bumped into a guy at Universal Studios Orlando last weekend who is LDS. He looked old and worn down. As we were talking, we both awkwardly gasped when we learned that I'm actually older than he is based on when we were in the MTC.

I asked my wife if a guy who looked that much older than her would have ever had a chance with her and she didn't hesitate to say no way. She's 9 years younger than I am.

So yeah, I have a younger wife and we look like a good age match. That works out today fine.
However, how many 17 year old girls would be interested in a classmate who looks like he's in 7th grade?
That was me.