As far as I know there's not really a universal timetable for taking next steps, but there's not enough info here to give any kind of opinion.
Age is a number, but it's a very real number. My husband and I are over 8 years apart, and it's amazing how different our frames of reference are regarding popular culture, how we were raised and just priorities in general. I can't imagine it reversed.
After all, I'm the mature one in our relationship. As he says he may have to get older, but he doesn't have to grow up.
I had a classmate in college who married a single mother who was 35. He was 22. I almost made a horrible mistake when I was introduced to her. She had a 14-year-old son, and I thought they were brothers and she was... well, you know. I mean, she had the same last name as him and all.
People judge by appearances. That's human nature. Our eyes trump our reasoning most of the time.
If it's true love, I wish the best for them. If it's not, well, they tried. I know you want the best for your friend, and the best you can do is listen, then support him or remain quiet. Voicing your concerns may not be received well unless he really does want your viewpoint, in which case give it to him but expect the consequences.
Somehow, I keep thinking of
Percy Sledge - When a Man Loves a Woman - YouTube
