Anytime, really. Every adult needs to have parameters in place as to who can make decisions should they not be able to. Once a person turns 18, there are considerable changes regarding who can access what personal information and decision-making. It’s a good idea to have a POA done for anyone 18 years of age and up since, by then, parents/guardians will no longer have access to nor decision-making power regarding finances, healthcare, and some educational records access.