It's not age based and you don't need a toddler bed at all. Toddler beds are a new invention. If you want one, fine. If you don't have extra money, just get a twin bed and side rails.
When to move your child? The key is to evaluate YOUR child.
First, he should stay in his crib at least until he starts to try to climb out. There is no need to move him before that.
Next, you have to weigh the risks of the different options. Yes, he can get hurt falling while climbing out. And he can get hurt wandering his room or the house while you are asleep. Some toddlers figure out how to undo baby safety locks and baby gates before age 2, some don't. Some parents are very sound sleepers, some wake with the smallest noise. Some toddlers will calmly do as they are told (for now) and some just want to see, do, and know no matter what you tell them. So you have to decide the best time to switch for YOUR family.
at 2:39 PM on May. 4, 2009