My girlfriend is 10 years older than me, but to be honest, I don't think about the years at all. It's a random passing fact that makes no difference.

Sometimes it makes for cute realizations, though. Liiike..

In a couple of years, we'll both be in our twenties. And we won't be in the same age 'group' again until we're both in our thirties. That's weeeiiird.

But in a cool way.

I think age is often used as an automatic judgement tool, but I very strongly believe that in the end, maturity is dependent on the person, not the age, and age difference only matters as much as the people in the relationship.
For me personally, I've felt that when someone is old enough to be my parent, it'd be a little weird for me to be with them. But I know other people manage it just fine.