Conversation so far:
when did Donnie Yen start martial arts?
He learned Tai Chi from a young age under his mother's tutelage.
who trained him?
his mother's.
how long did he train?
CANNOTANSWER.
Are there any other interesting aspects about this article?
His exposure to mixed martial arts (MMA) was heightened when he went back to the United States from 2000 to 2003.
how was it heightened?
While making his Hollywood debut, he also took time off to learn the various martial arts forms.

Question: what were the various forms?
Self-contained rewrite: what were the various forms of martial arts that Yen learned?