We were just having this conversation the other day. Jack seems OK in it still, but it's getting REALLY heavy to lug around...and he's not even as big as his brother and sister were! I think I'm going to have to shop around for a good convertible seat pretty soon.
Jenna stills sleeps in hers and still in it for stroller and car. Shes 5 mths old. We do have convertible car seats too
I don't really remember either, but with the other 3 it was around a year old.
With the other 3 kids, we carried them into stores and other places in the carrier until we quit using the carrier.