For me, it's always been irrelevant. I wasn't raised to put importance on it. Other than, to respect one's elders. Though, having had an abusive mother (fortunately, I spent much of my time with my grandma), I came to realize, it's something which needs to be earned, not, given automatically. 

It matters more to me how I relate to a person. Which is probably why, just like my interests, my friends are quite diverse. To be honest, it didn't always include age. Being an only & coming from a stricter religious upbringing, except for kids in school, the people I associated with were my parent's & grandparent's age. That may be a big reason why, for much of my life, I naturally gravitated toward those who are my senior. My ex is 15 years older than I am. We're still good friends & have so much in common (views, beliefs, interests), I joke that we're practically twins. In the past few years, the age range for friends has opened up. I now have friends from 18 to 75.

Ever since chat rooms & apps became popular, one thing people ask is, a/s/l. Meaning: age, sex, location. I don't mind admitting my age, almost 53. Still, I was raised that's not something you ask people. I don't. I figure if they want me to know, they'll tell me. Besides, the way some people look or behave, they might come across as older or younger than they actually are. Do your friends tend to be around your age or does it vary?