I know of a Stallion who was gelded at 15. It seemed to take some time for
all the hormones to 'drain' from his system. I'd say nearly a year or so,
but now he's a pussycat and as time goes by he just gets sweeter.
Same thing happened to my dog who was 'gelded' at nearly 10. He stayed very
much his studly self for nearly a year. Now my spayed female lab mix is more
butch than he is.