2 month old supported sitter?

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My son will be 2 months old on the 29th and he's already trying to sit up. He still needs support though. I'm wondering if this means he should start baby cereal soon? He's breast fed, sometimes by bottle. And lately has been eating every hour from the bottle. I'm wondering if he's not getting full .. a couple days ago he was going 3/4 hours between feedings . Anyone else dealing w this?