albino checkered won't grow - 10mo+?

[bohemianfreedom]

It's my son's snake. he's at least 10mo old but only about 9-10inches and barely a pencil width. He eats feeder guppies about 1 every 2-3 days. I've tried feeding him more but it won't. I just realized for I don't know how long the UV lamp has been shining mostly through the glass and not directly over the tank...could this have stunted his growth? He is generally pretty active and seems fine other than I think he must be undersized