A proper friend as well, not just a neighbour or that man you sometimes speak to at the post office.
I have a friend (45) who’s almost double my age (23). We work together, but we will often go out to bars and I will sometimes go to his country house for a weekend. We are on a fairly similar level at work, so it doesn’t really feel that weird in terms of superiority. Without wanting to sound patronising, I have found the whole thing quite valuable.