at the height of one's powers

be at the height of one’s powers (if someone such as a great writer or musician is at the height of their powers, they are doing the best work of their whole life) — на пике своих сил и возможностей; в расцвете (сил, таланта, возможностей)

Example 1: When Orwell wrote 'Animal Farm', he was at the height of his powers.

Example 2: The film shows Jimi Hendrix, at the height of his powers, giving a brilliant version of 'All Along the Watchtower'.

see also
[в расцвете]

[over the hill]
past one's prime
He is now past his prime.
[over the hill]