A very common phrase: être en plein forme

Comment ça va depuis ton opération ?

Je suis en pleine forme.

Some more colloquial phrases:

1. péter la forme
2. avoir la pêche/la frite/la patate

Too long for a comment. Of course “péter la forme” as a translation of “alive and kicking” is not so bad, but it misses a key point of that English expression, related to the “kicking” which means almost literally that, nonetheless you are alive, but you are also able to kick a ball as a player, say a basketball player.

An other important point in that expression is that it is twofold: first you are alive, but, much better, you are kicking. I would suggest

— Comment allez-vous ?

— Ecoutez, je suis en vie et performant.

For a person (especially an old one), you can say “bon pied, bon œil”.