As long as he is physically active (enjoys hikes), patient (not a busy, crazy kid), and doesn't have a fear of heights, he will love it. There is a decent amount of patiently waiting for the group/taking turns and listening to the tour guide. It is fun, but much less a ropes course, and more of a small back stage/personal tour of the animals at the park. Is he a picky eater? My kids wouldn't have touched most of the food with a 10 foot pole ; ) Yours might be more adventurous. Not a huge component of the experience.
So...my advice is to be honest with your kiddo about the age requirement, that he is younger than they prefer, but that it is safe for him (and it is). Let him know that there is a chance that he may not get to do this, and if he can handle that without being destroyed/heart broken, then sign him up!