Jason is the tallest person in the Batfam. He’s even taller than Bruce. When Dick tries to pull seniority he is not above saying “I’m bigger than you”.
Additionally: Tim is one of the smallest. Literally all the bat boys will be taller than him as adults. Cass, Babs, Kate, Selina, and possibly Kitrina are all at least a little taller as adults too. This is mildly frustrating for him.