ok. i see the neuter thing has been stated. also, how many cat boxes do you have in the house?
there should be one for each cat and 1 extra.
you said the cat is 2.5 years, how old are the other cats?
i rescued a little one last year. the 2 current residents are quite a bit older than him.
they only get pissy when i'm outside with them, but when i'm not in eye sight, they will play with him.
also, find an orange based neutral cleaner, to spray in the areas he goes to.