Hi,
Does he do this with kids his own age or his sister? Or is it just older males?
I'm going to assume it's just older males from what you've said here. Some of which is pretty normal I think (my kids did it a bit and so do younger boys around my boys). I think all boys try to gain dad's acceptance and approval ... maybe just a head's up to Dad to be aware that your son is putting his own needs and likes after dads.
One of my sons pretended to like fishing (obviously didn't) so he could join dad and the other boys on trips. I just had to mention to Dad that he needs to do some things each child likes to do, and join them. That really helped.
With older boys, kids just want to be accepted by them .. so they will try to emulate them a bit. It's that typical looking up to older kid thing they do. I heard one of mine say he didn't like a TV show that I knew he loved, because an older boy said it was stupid.
I took that time to have a little talk - that they should be proud of themselves, their choices, their likes .. and that if someone doesn't respect or appreciate that about them, then they are not really a friend (or the best fit). That helped mine a great deal to sort of wean out kids they were just trying to impress.
Sports and activities helped mine gain confidence - standing out on a team (even if it's only once or twice a season!), doing things on their own in front of others (piano, etc.) and groups such as cubs were great. I'm sure you've already got him in some of the things he is interested in. Even swimming lessons (mastering a level) gives them confidence.
Good luck :) I think recognizing this in your son is great. Talking to dad is where I would start (some men kind of like that kids emulate them, and just need a reminder that boys need to be encouraged to express their own individuality).