Giving unsolicited advice to your adult children (specifc question - but curious about in general)

I don’t think you have to give him “advice.” If such advice was given to me, at least now in my older years, I would double down – break out the sandals and black socks.

I think you can do a couple of things. Make it more of a joke – “you have no fashion game.” Or just buy him stuff for holidays, birthdays and such.