Train them at an early stage. Because

Hi

Are these lines fully natural, especially the red parts? I have taken them from someone's lecture.

(Talking about training/educating children)

We should train them from the beginning...at an early stage of their lives. Don't wait for 'when they are old enough'. Because by the time children are in their early teens, their habits are so well-ingrained that it's almost impossible to change them.

Thanks,

Tom