First time mom, is it normal for a 6 months old baby to..?

hello po, my baby is premature(2 weeks early) he's now turning 7 months old but I noticed na parang di sya ganon ka-active and liksi gaya ng ibang kaedad niya. Di niya pa kaya umupo nang mag isa, unlike other babies. Is it normal po? Sorry, I'm a teenage and first time mom, sooo. Anw, thank you for the answers!