FWIW, places like T-rex and Rainforest can be very hit or miss when taking little kids. We took DS at 3 to our local Rainforest cafe and he barely made it through ordering. Before our food came DH had to take him out to the mall's food court, and i had our food boxed up, paid, and left. Ate at the food court.
Next time, at RFC at
Disneyland, he did a little better, but still didn't ENJOY it.
But then as he got older he wanted to eat there, and he does better now. But not if we're sitting right near something that makes noise.
We went to T-rex when he was 6 or 7, and it was borderline overwhelming; he would have appreciated earplugs. So would I, actually. The only thing that got him through the meal was the fact that we were surrounded by herbivore dinosaurs, not carnivores. Even at 6 or7 he was still a bit worried that they weren't REALLY animatronic.

And it is INCREDIBLY noisy in there.
so go, and if he does well, YAY! But also be prepared to leave if he gets too overwhelmed. Have a plan; who goes with him and who gets the food boxed up, etc. Makes those quick exits easier if no one is having an issue with the concept of leaving, and if no one feels put upon to do whatever they are being asked to do.
Hope that helps!