A La Secondes Drills from Just For Kix 

In ballet only male dancers do secondes, mostly, female dancers do fouettes.

You can start whenever

Rachel Schumacher intermediate lyrical

Start doing these exercises now, but don’t practice the turns without a teacher to correct your technique. You don’t want to build bad habits! Build muscle instead and when you get there the turns will be a breeze :)

The traditional leg to turn on is left, you should start (if you haven't already) training on that leg :)