My kids are 12-10-9, and we'll turn it way down--not sure what temp it actually gets to, at least 98 if not a tad below. Last summer when it was new, they put their goggles on and swam around as best they could. Thankfully they have mellowed out with their first year of tubbing under their belts. Now they pour tall, ice-cold waters, and hang out while playing cards. Or they just hang out with a friend for a good hour, just soaking and chatting.
We go through a LOT of Dichlor keeping it clean, (lotions, hair potions, other people's gross unclean kids) but hey, it is being used and enjoyed, by all!
In the winter, we keep it around 102, as then the whole family can enjoy it together for awhile. I count on the cold MN air to chill it a bit so we can stay in longer.