My little guy was too short for a lot of stuff on his first trip and it was a major bummer.
But the good news is, some of the rides gave him special fast passes to bring back when he got taller and he's excited to cash in his Test Track fast pass in a few months (we've been since he was tall enough but that was while Test Track was down for that long stretch).
Also, on the next trip when he was tall enough, it was a BIG DEAL and we made a big fuss and took pictures of him GRINNING next to the height things at every ride and the CMs joined in making it a big deal. It was really nice. So there's always something to look forward to!