Is Mizu from a 13" line, or is he 13" right now? :hi:
Our Myra has anonymous parents, but we are assuming she is a 13" because she is about 11" now, and 19 lbs. She is 11 months old. 29lbs as a pup for a small Beagle seems a bit high, but really all dogs are a little different.
From reading about Beagle health, the general way to tell if they are overweight is to look down on their back when they are standing, and if they have a noticeable hip/waistline they are OK. Also, a defined ribcage line is good to find. If they have a little extra padding in these areas they may be getting overweight. Hope this helps!