Well let me get one thing straight. He is turning 19, so I now see it possible that he is just growing late. Though he seems to have matured rather early. At 15 he was fucking strong, physically taking on big black dudes in arm wrestling and shit. He was never really eat at one point he may have been like 5-10 kg over-weight a few years ago. So I would rule out the gaining an inch by losing weight.
Anyway, now I am turning it over to my side of the story. I'm into boxing, been doing it for quite some time now. We have alot of cardio and power(heavy weights in short bursts) training.
I don't take any sort of supplements. I rather be all natural. ;-)
My regular diet restricts me down to being vegetarian. Sometimes 2 eggs for breakfast, and very rarely some meat(boneless, beef, chicken, pork) in the last 1-2 months, I've almost stopped drinking milk as it gives me a bit of flab on my belly.
So anyway 1-2 days ago, my girlfriend was sucking my cock, I realise I was some how 1 inch longer and my girth was still the same. xD
I was 7x6".