Speaking of lame concerts (someone above mentioned seeing the Captain and Tennile....), when I was in college (I think 1974), my girlfriend (now my wife) and I were prevailed upon to take her little sister to go see the Jackson 5. It was in a "theater in the round" venue in the Chicago area, with a rotating stage (Mill Run Theater, I think). I'm not certain how old Michael was - but he was basically in his early to mid-teens. LaToya was also in some of the numbers, and Janet was maybe around 8 or 9 years old, and brought out for a couple of songs.
At the time it seemed incredibly lame to me, but in retrospect, it now seems kind of cool to have seen the full Jackson 5 live. And they WERE pretty good....
Later edit - in looking at some listings of Jackson 5 tours, it was a one week engagement at the Mill Run Theater, in June of 1974. In all of their other tours, from 1970 to 1976, the J5 played larger venues, typically. In 1974 they played longer engagements at smaller theaters, often "theater in the round" venues.