You need to do what everyone should do when in a relationship that's becoming serious.
Think about the future and discuss it.
Age gaps, in themseleves, don't bother me in the slightest. But when it's this big. I always think of kids. If you wait a few years to have them he will be 60. Do you want young children with a man in his 60s?
You are likely to become a fairly young widow. And your kids will lose one of their parents young. Yes I know that can happen to anybody. But the chances are far higher if he is pushing 60 before you have them.
My dad is a fit healthy 60 year old. He runs half marathons etc. I had my first when he was late 40s and my second in his mid fifties. I have seen that he finds the younger over far more difficult that the first. The 7 years made a big difference. He adores them both. But you can see a difference.
Me and dh cared for 3 of his grandparents. Dhs mum wasn't interested so we shared care with his dad. And now helping care for one of mine. I have 2 aunts and mum that I share care with. So it's not that hard, but it's not easy either. And non of these relatives have lived with us. My mum is 60. By the time I have finished caring for my grandad I will be starting to care for her. It's really difficult to work, have young kids and be a carer.
Do you want kids at all? Maybe you don't so it's not an issue.
You may be happy in just living in the moment. Which is fine, too. But you need to think about things before you move in together and decide if you are happy with that future. But everyone should do that. Regardless of age gap.
I can see why your friend is concerned. But if I was her I would express them once (if I really felt I should) then shut up and let you make the decision yourself.