Yes, three male platies can live together peacefully. This is because platies are generally peaceful fish and do not display aggressive behavior towards each other unless there is a lack of space or resources in the tank. When kept in an adequate size aquarium with plenty of hiding places and enough food, 3 male platies get along just fine sharing the same tank. However, it's important to keep an eye on them for signs of aggression such as fin-nipping or chasing. If any of these behaviors occur, you may need to add additional decorations to create more territory boundaries or separate the fish into two different tanks. Additionally, if you plan on adding female platyfish to this group then it’s best to have at least 2 males per female so that they don’t become overwhelmed by too much attention from one male in particular. Overall though, keeping 3 male platies together can work out very well when done correctly!