He had been playing table tennis since he was six years old.

[Alice Chu]

Are the sentences below correct?
1. He had been playing table tennis since he was six years old. It was his favorite sport.
2. He had played table tennis since he was six years old. It was his favorite sport.

 

[5jj]

Both are grammatical.

 

[emsr2d2]

If there's a good reason for the past perfect/past perfect continuous, they're fine. If he still plays table tennis, use "He has been playing ... since he was six".

 

[Yankee]

Both are OK, but each suggests the possibility, that additional context would mention, a reason the activity ended.

 

[SoothingDave]

And boy, are his arms tired.