I'd say probably about 8 months
As long as they have there first shots I plan on taking my little one in at 3 months
I've seen people being little newborns like a month old into pools the earlier the better it's good to get them used to it early but indoor would be best cause their not really supposed to be in the sun much till 1 year old
In my opinion I think they should at least be 6 months. But idk that's when I took my kids in the pool or older