I married someone 5 years older, so I put +5. But, to be honest, as long as they are somewhere AROUND my age, I don't care. I think having common interests and attitude is more important.
...
Being able to enjoy the same types of things is very important. ... We have common interests and approaches. ...
I'm not sure that someone 20 years younger than I would really have the same attitudes or frame of reference that I have; I think it would harder to find common ground. However, it's not impossible, not by any means. I just don't think it's as likely.
Agreed. I also chose +/-5. My wife is 2 years older than I am, but then, we share a lot of interests and views on life. We even met through a common interest (medieval re-creation), and 20+ years later, we still have lots we like to talk to each other about (books, movies, things we're learning, hobbies) in addition to the usual day-to-day stuff.
Before I was married, I dated a woman who was about 4 years older than I was. (Honest, I didn't set out to date older women. Most of the time, it was women 1-2 years younger. But the outliers are interesting...

) She constantly refered to the age difference, and thought I should just follow her lead in all things, due to her "greater experience". That got old very fast.
The older you get the more fluid your range becomes and the less difference the age makes. If you have a big gap though at some point the older person's aging issues, whether in looks or life choices or health can potentially cause relationship issues. Yes I know people will say it shouldn't matter, but issues arise just like the do for other differences between people such as religion or culture.
Yes, there are definitely times of life where physically/psychologically, people are usually in very different places than someone 10 years older/younger than they are. In the middle years, 10 years isn't as big a difference; but it can be in the late teens/early 20s or the later part of life (with more health concerns, for example).
My test would be..
Me: Do you like Lady Gaga?
Dude: It is TOTAL CRAP!!! (has never listened to it other than in the background of course)
/ GONG!! Good bye.
I'm fairly
meh on her pop music (that I've heard), but I did enjoy the duet she did with Tony Bennett. So I think she has an amazing voice, but I don't care for a lot of what she sings. Wait... does mentioning Tony Bennett make me an old fogey?
I think if Jurassic Park was made before you were born, or you lived through the Jurassic period, you're too young and old for me, respectively.
Star Wars seems to be an easy touchstone. We have a friend who was taken to it when she was a babe in arms. I went to see it as one of my first dates in high school. There are often times when she just doesn't get a reference that my wife or I make, that we have to circle back and explain. I can't imagine dating someone who didn't share most of the cultural milestones with me. (That "common ground" that
auntiehill described so well above.)