Most kids will outgrow it by height before weight. To check to see if it is still okay for height, there needs to be at least 1 inch between the top of the head and the top of the plastic shell. So, legs can overhang without a problem, but check the head.
You'll want a convertible - something that rear-faces and then forward-faces. It's safest to keep the baby rear-facing until the limits of the seats are reached, not just the 22lbs and 1 year that you often read about. Most seats rear-face until 30-35lbs.
The Briatax Marathon or Boulevards are great and will let you rear-face for a long time and then forward-face for a few more years.
As for when your baby will hit 22lbs, who knows . How old is she or he now? My DS1 hit 22lbs at about 10 months, but outgrew his 22lbs seat at 7 month by height. My DD hit 22lbs at about 1.5 years and outgrew the seat at about 12 months. Both kids were 14lbs or so at 3.5 months. DS2 was 14lbs at 3 months, but is only 18lbs now at 6 months.