Since I know a lot of folks younger than 70, I would say that most of my friends are 5 years or more younger than me. Sorta works out that way when you are nearly 76.
Of course, most of my friends are still way older than you! Yeah, I’m talking to you!
I miss-voted - “Most are older” when I meant “most are younger” - around 7 years younger is about the median, I’d guess, quite a few are about to turn 40 soon.
It’s just happenstance that a lot of my immediate contemporaries from Uni went overseas afterwards, so when I got back to my home town after a couple years slaving on the mines, I turned to the then-currently-studying crowd in my old Uni societies for roleplaying groups and nightclubbing mates. And they were the ones running the SCA group as well.
Last night went to a wake for a friend/ex cow-orker. He was 9 yrs younger than me. While there, I re-united w/ 2 other ex cow-orkers who are also 5-10 yrs younger than me. We all expressed a desire to see each other more frequently socially, and are all situated to make that happen. So maybe I’ll be able to change my previous “vote”! 
And after, went to a family gathering. A lot of family is in town for my FIL’s 90th birthday. Sat next to a 27 yr-old niece. I really enjoy spending time w/ my nieces and nephews who are 25-35. Really like to hear their perspectives, and gravitate towards them during family events. Am definitely on “friendly terms” with them, so I guess that would affect the average age of my “friends.”