Yep, what 3beans said.
Most seats expire in 6 years. The primo viaggio infant seat does expire in 5, and *some* of the dorel seats claim an 8 yr expiration, although not any of the infant seats, I do not believe. I do not know of ANY seat that expires in less than 5 years. You should be able to find a date of manufacture and an expiration date on your seat. If it IS graco, then ytes, it is a 6 year expiration, so would probably last through this baby. But again, if it is a 3 point seat, ditch it and get a 5 pt one. REALLY.