Hi
my kitten used to do this too,
remember kittens dnt have as much staminer as adult cats so they get tired out quicker, plus because he is a long haired cat he can also start to get very hot as he plays, its not only dogs that pant to cool down, normally cats like to lay on something cool after playing, like kitchen tiles or something.
Just keep the play session small and build them up over time, also it an idea to keep them short in hotter whether to, plus grooming will help keep him cool by removing all the extra fur and stopping matts from forming, it also creates a clearer path to his skin for the air to cool him. i hope this helps, best of luck, Amy