Growing Up! Slimming Down?

On my way to the helicopter last night, I called Napi and got the latest specs for Mr. Ami'. Unfortunately since I was driving, I couldn't write down the specs. I can't recall the exact numbers, but he's hovering around the 80th percentile for height, and the 30th percentile for weight. Considering he used to be in the 90th percentile for weight, that number is a little alarming. I guess it's better than being overweight, but I can't figure out if being underweight (if that's what these numbers truly mean) is a good or bad thing at his age. Anyone know the word on this? Napi (and the doc) don't appear to be worried about it, so I guess I shouldn't be...