Worried about 18 month olds weight

Nicole • 10.03.15👰🏻💍 - 06.06.17 👦🏻💙 - 07.03.19 👶🏻💜

My son had his 18 month old check up today and he literally has gained 1 pound since June! He’s 21 lbs but eats like a little piggy and is very active. Loves veggies and pasta but not a huge meat fan. The doctor doesn’t seem worried just that he’s burning it off being so active but kinda freaks me out bc I have friends with 6 month olds 17-20 lbs! Anyone else have a light weight??