Question

i _run very fast. when i was 4 years old . (past ability )​

Answer 1

Answer:When  I used to run fast when I was 4 years old.

Explanation:

MODAL VERB:

Modal verbs are auxiliary verbs (also called helping verbs) like can, will, could, shall, must, would, might, and should. After a modal verb, the root form of a verb is generally used. The word to should not appear after a modal verb. An exception is the phrase ought to, which is considered a modal verb.

Answer 2

Answer:

I USED TO run very fast...