This sentence looks strange. Is it correct and would this be the most common way to ask it?
Don't use the pronoun. It's clear who we're talking about so you should say "Cand incepeti sa fugiti?".
You could also say "Cand fugiti?" if you want to shorten the sentence. It may make it seem more casual/informal though. Use this with friends.
Great, simple explanation. Thanks.
In general the pronoun is not needed but the current form is correct and widely used also. Think of it as "what about you, when do you start running?"