I'd say neuter him.

I do prefer intact males - Ronin was intact for the first 4.5 years of his life. However, if you aren't going to breed him, IMO he's had enough time to mature.

Yes, their metabolism does slow down. That doesn't mean they get fat, it just means they don't need as much food.

Ronin was a heavily muscled, intense, protective intact male. Now, after being neutered for nearly 2 years, he's still a heavily muscled, very intense, extremely protective dog... just with more focus!

If a dog is "ruined" by neutering at a mature age, it's my personal opinion that *that* particular dog is lacking in the temperament department. Ronin didn't need "little swimmers courage" - he's a true Doberman, balls or not.

(side note - Ronin didn't roam, he didn't inappropriately mark, etc. He was a very good intact male. Neutering him was the icing on the cake. )