Re: "He's so skinny!" and "He's so tiny!"
If he's healthy, yep. Happy, eating well, wetting and dirtying diapers, seems alert there's probably no problem. Babies don't need rolls of fat to be healthy, and we all come in different sizes. There's such a wide range of normal.
There are two little girls at our playgroup. They're about 5 weeks apart, they couldn't be more different, but they're both normal range. One is 17 mos, JUUST barely 20lbs, if she even is that heavy - she's very petite. There's not a spare ounce of flesh on this child. She wears the same size clothes as my 9 month old (12 mos, and she can fit into some 6 mos stuff), has only 4 teeth and hardly talks, but she started walking at 9 months and now is running absolutely anywhere - she's just a busy kid. The younger one is 16 mos, 31lbs and still has a lot of the baby rolls to her and is quite tall to go with it, full mouth of teeth, has not only several recognizable words but is stringing them together already, but she's only just now starting to walk. Normal is an enormous range, and that's awsome. Because honestly if we were all the same, it would be pretty dang boring.