I can only assume you mean his anus.
(Really, real terminology is helpful. Endless slang that means little to anyone else just tends to muddy things up.)
How your partner does or doen't respond to anal stimulus is going to be individual, just as its individual who any person responds to a given type of stimulus or area stimulated. Orgasm is whole-body: so there aren't orgasms for areas -- they still happen primarily in the entire nervous system, with genital effects. In other words, there are not anal orgasms or clitoral orgasms or vaginal orgasms, etc. There iso or gasm which may be reached primariyly or solely via stimulus to those areas, but orgasm is still whole body. Your partner may or may not reach orgasm from anal play alone, and if he does (from anal play alone or anal play combined with something else) it may take any amount of time, again, just like orgasm from anything else varies from person-to-person and day-to-day.
Anal play is highly unlikely to damage the prostate, as the prostate can't actually be reached via the anus: anal play simply stimulates it because the prostate is located inside the body in such a way that stimulus to the anus indirectly stimulates it.
Injury or pain is more likely to be to the anus or rectum itself, and when a partner is doing very gradual play (per size and depth), using PLENTY of lubricant, employing safer sex practices AND both partners are communicating clearly throughout, injury is unlikely.
(Also, any toys used MUST have a flared base -- unlike the vagina, things can get trapped inside the anus otherwise.)
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