if u want a literal translation i would choose A option, Cuando tenia 10 años...as it is the same as when i was 10 years old. Option B is way different regarding meaning, as an example: Hacia 10 años que no la veía. Hacía tanto tiempo que no viajaba en tren, both sentences are totally correct, buy they do mean something different than "when i was xxxx" when we say hacía (1, 2, 3 10, años) que no (an action) what we are saying is: Hacia 10 años que no la veía >>>>>>>>>>It's been 10 years without seeing her(note: that this is not a literal translation, though same meaning) Hacia tanto tiempo que no viajaba en tren >>>> it's been ages without travelling by train(note: once again no literal translation here, but same meaning is still respected). Going straight to the point, When i was 10 years old=Cuando tenia 10 años.

La A y la C son correctas. La B es incorrecta.

Hola Andy. The right answer is A: "Cuando tenía diez años..." We use the verb "tener años", instead of English language that it is used "to be years" Saludos. Antonio

yo necesito aprender español por favor