If your child is active, playful and reaching the corrected age milestones, then don't worry. Would require a few more details such as birth weight, how many weeks preterm. Weight doubles at 5-6 months and triples at 1 year. So even if your child was 3kg at birth, at 6 months he has more than crossed that mark. So you're feeding an adequate amount! The exact amount of milk depends on the baby. Force feeding will lead to food rejection. Maybe offer milk in an open steel clean cup instead of the bottle. If bottle is what you prefer, make sure to change the nipple every 2 months. Also need to know what he is doing developmentally to assess whether he is ready for solids. There are 4 solid readiness signs to look out for before starting solids. He should complete 180 days corrected age (since premature birth) before starting. You can read about it on my Instagram page also. For any queries, kindly book an online consultation with me. I am a lactation consultant, IYCF (Infant and Young Child Feeding) nutrition expert with an interest in Childhood Infections and Vaccinations. You can check out my Instagram page @drbabymum for helpful tips ! Take care!