We don't have air-conditioning in the gym and I believe temperatures get to maybe the mid 80s (Fahrenheit). We don't have a thermometer and I'm bad at estimating heat so I can't tell you for sure. We have fans and take a lot of water breaks with kids during rec classes. Team just carries their waters event-to-event. We also have 3 truck doors (as the gym is in a warehouse type business park) that we open everyday.
We are in the south... 100+ degrees most days! Morning practices are better since the gym is a little cooler, but ours is a big metal building as well. I remember going to my first meet where it was FREEZING inside and for some reason (probably since it was what I liked), I loved it. My advice is to give those gymnasts the advice to hydrate hydrate hydrate! Fans won't do much for us, but if it gets to the point where someone feels weak from heat+exercise, I'd say thats too hot. Believe me, I know what it's like to do an hour of Plyo combined with the heat of July. Georgians know us some heat
I train in a sports centre which was designed by someone who didn't think about the weather. We have a very high ceiling and windows lining the top of the walls. This means that in winter is is FREEZING and in summer we get to sweat it out in the greenhouse that they (I hope) inadvertantly created.