A 5 month old should be eating adult mice by now. But like Jenn said the feeder should be no larger than the widest part of the snake. Its pretty amazing what they can get down though. You should really switch to frozen thawed feeders to lower the risk of the feeder harming the snake. I purchased a bag of 50 adult mice from rodentpro.com and I havnt had a problem yet with my ball eating them. Hope this helps.