when you were
Ты мог считать до десяти, когда тебе было два года.
You could count to ten when you were two years old.
When would be convenient for you?
Когда тебе было два года, ты уже умел считать до десяти.
When you were two years old, you could already count to ten.
Где ты жил, когда тебе было тринадцать лет?
Where did you live when you were thirteen years old?
Ты умел кататься на велосипеде, когда тебе было три года?
Could you ride a bicycle when you were three years old?