Age does not matter what you need to feed is a prey equal your BP's girth size (widest part of your BP's body).

A few things to keep in mind with a newly acquired BP is to feed the same type of prey for at least a few feedings (3 to 5) before attempting to switch. If the animal is fed live feed live before attempting to switch to F/T. Obviously switching is easier when done one step at the time, live mice to f/t mice or live mice to live rats.