You can go in and use the equipment with and they won't say anything. As long as you follow the rules your ok.
Noone ever enforces it. I think the rule is there so a bunch of rowdy teens don't come in without little kids and get crazy. When my son was in 11th & 12th grade he'd often come and play with him little brother and sister (they were about 4&6 at the time ) and no one ever stopped him. I jump on trampolines with my kids often even now.
12, but when it is not busy I have seen older kids and adults on equipment. Especially with younger ones.
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