I have no kids but looked it up online and one site said that kids are usually ready to START potty training at about 2 years, though there are no rules to it. You can train them earlier than that if you like. They also said that boys usually start a bit later than girls.
They also have something called "Pull ups" now which my sister used with her kids which encourages the whole potty training thing. They're not quite underpants and not quite "nappies"!
TMI, I know, lol.
I agree that it's best to keep untrained children out of the common pool areas. A man at my apartment complex had his two DOGS in the common pool once and I just about gagged. Ew. I had to ask the manager to please do something about it and he even complained when told he had to get his dogs out of there! SOme people just don't get it!