Top of his game

he was writing at the top of his game what is the meaning of this phrase which is said about a writer.

thanks

It is said about a lot of things. Whatever vocation or path in life a person is most associated with or known for is "his/her game." To be at the top of it is to be the best he/she has ever been in this profession/sport/vocation. I hate using slash/vergula this way, but any other way is just as confusing. Would you like a translation into actual English?
SS

At his or her peak or prime.