Tom has been playing tennis since he was twelve.

[Alice Chu]

1) Tom has been playing tennis since he was twelve.

2) Tom has played tennis since he was twelve.

The first sentence above emphasizes the ongoing action, playing tennis, and the second emphasizes the starting point, twelve years old. Both the sentences mean a repeated action of playing tennis started at the age of twelve and continues in the present. It isn’t necessarily happening at the moment of speaking. Is my understanding correct?

 

[Tarheel]

I have been playing chess since I was ten.

That means I started at ten and have been doing it ever since.

Your analysis of the second sentence may technically be correct, but I can't imagine anyone phrasing it that way. (Others may have different opinions.)

 

[SoothingDave]

And boy are his arms tired.