At about 13 years old

[Rachel Adams]

Is each sentence grammatically correct?

1. "He started drawing at about 13."

2. "He started drawing when he was about 13."

3. "He started drawing when he was about 13 years old."

4. "I started drawing about 13 years old."

5. "He started drawing at 13."

6. "He started drawing at 13 years old."

7. "He started drawing at about 13 years old."

 

[teechar]

4. "I started drawing about 13 years old."
6. "He started drawing at 13 years old."
7. "He started drawing at about 13 years old."

Those are no good. Try "... started drawing at (about) 13 years of age".
The rest are grammatical.