Well, my husband and I have a significant age difference. (He is 44, I am 23) However, I pursued him, he didn't pursue me, and we ended up just working together as a couple. 

Before that, we met at work and worked together with him as my manager for about a year, then I got promoted, got my own store, and like 5 months later we started dating.

I think it really, really depends on the person(s) involved. However, I don't think it's wrong to be uncomfortable, my friends and family were slightly skeptical until they started to know him and sat down with him, he hasn't given them, or me, any reason to believe otherwise. There's no manipulation here, and while there's a little difference in certain things, we share similar hobbies and just love each other and our daughter. 

At the end of the day, you're there for your friend, not his girlfriend. I'd support your friend with skepticism until you see/know more. It's still early in a relationship, there's still a lot of New Relationship Energy to work out, I wouldn't judge it based off of age alone as some people may surprise you.