I'd go for it, if you want to see if it makes any difference to his behaviour you can get him a Suprelorin implant (injected like a microchip) which lasts up to a year - I did that with my boy as I left it really late and it worked a treat!
With male dogs beyond population control there is no benefit in doing it in a young dog and a middle aged one. I would make sure he has had plenty of time to settle in with you before he had the op though.
I have a yellow labrador that I got six months ago. He is almost four and a half, but has not been neutered by previous owners. Are there any problems associated with neutering at this age or should I just go ahead and do it? Have to say, his balls are rather unsightly, so I'd be glad to see them go!