i dont belive there is such thing as a healthy undersized snake. aslong as it has good muscle tone eats drinks and doesnt have any lose skin they will grow at there own rate.
if you are conserned about its wieght wiegh him on some digi scales measure the length of it and post it in a new topic on her so we can find it easily.
me and kazerella both have what some people may say to be undersized hoggies but we both know they are completely healthy