My daughter is almost 9 months but still pretty small - 17 pounds. We can carry her easy enough and it's nice to just pick up the whole carrier when she's sleeping, but I think I want to move to a rear facing convertible soon.
When did you guys make the move?
[Poll]
Re: What age did you/are you moving to convertible seat?
med-free birth x2, breastfeeding, baby wearing SAHM
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We moved her at about 6 months because she'd already outgrown the infant seat! The straps had gotten too tight and she didn't look comfortable anymore. She was still under the weight limit but she's round
She loves being in the bigger seat 
He didn't like being reclined any longer at that point, and was MUCH happier in the convertible.
I just wanted to mention that we have the Symphony 65 and it's weight ranges for use are 5-100lbs. It can be used in 3 different configurations starting as an infant (which I wouldn't do) and goes through to a booster seat. I believe DS was 17lbs when we started him in the seat and he did great.
this
A kiss he will never forget- Disney World 2014