DS is still fitting just fine in his infant carseat, but I do think that he won't fit in it past a year old (we have a big one). I am looking into convertible carseats right now.
Some have a minimum weight of 22 lbs, then they last longer or can convert into a booster.

Whereas others can be used with infants (5 lbs) but the ones I'm looking at only go to 65 lbs.

How heavy was your LO when you switched them to a convertible/booster carseat?

Do most kids even reach 65 lbs before they don't have to have a carseat anymore?