Getting a 450 CC bike may not be the best idea if you are starting to ride a bike. The reason is that these bikes are too powerful to be controlled by an inexperienced rider. Also, not being able to control and ride your first bike can put you low on confidence, making you dislike the concept of such bikes. So, start on a smaller bike. Many adult professional riders who have been in the sport for years still use a 250 CC bike. There’s no reason to start with a 450 specifically.