My oldest was 40 inches well before age 3 (he just turned 6 and is more than 50 in - he's on pace to be 6'4" plus.)
My middle DS has a heart disease and it's affected his growth. He was 38 in at the cardiologist last week. He'll be 3 in two weeks. He's my daredevil so it makes me sad that he can't do Splash Mountain. He'll never be able to do anything more intense than BTMR and Splash anyway.
My youngest seems to be falling in the tall category, like his parents. I am not sure of his length but he was 19 lbs in June as a 3 month old! He's wearing 12 month clothing easily and they barely snap.