I don't believe that we have an age limit per se but we do ask that under 18s are accompanied to apiary meetings by an adult and that the guardian signs a release form. The biggest pain we seem to have encountered so far is around photography during apiary meetings when there are kids present although that might be the committee over reacting to the usual badly worded legislation.

From a practical point of view I don't think we've ever had a situation where 5 year olds were in the actual apiary area, at least not when I've been there but we put the onus firmly on the parent to accept that while kids are welcome, we can't guarantee that they wont get stung and they accept that photography might be going on while the hives are open. Outside of the apiary itself it's not uncommon to have a variety of kids of all ages from toddlers upwards hanging around the place.