Translation:I have been playing baseball since middle school.
Yes. Because the sentence has "から" which shows a starting point in the past and "しています" which shows that the person is still doing it now, we would use "have been."
(I am/she is/they are) studying.
(I have/she has/they have) been studying Japanese since July.
(I am/she is/they are) watching.
(I have/she has/they have) been watching TV since 8:00.