Most carseats expire 6yrs from the date of manufacture. There are a few on the market that are 8, but again general 'rule' is 6yrs. If in doubt, call the manufacturer and ask. I know that Evenflo is 6yrs though.
ANYWAY, do NOT give the seat away, cut the harness straps, remove the cover, and write 'DO NOT USE' in black marker on the plastic and THROW IT AWAY! It may seem like a waste, but it has served its life.... 7yrs is a long time for a piece of plastic. So get rid of it safely (cut straps, remove cover, write DO NOT USE on it) and call it a day. Plastic goes through a process called photodegeneration, much like the plastic toy in your yard that gets faded and weak in the sun, the same thing happens to a car seat over time. Of course hte plastic is of higher grade, however its still only plastic and can only hold up to so much, that is hwy they expire, and why they are not safe to give away after the expiration, or a crash.
You can buy a new evenflo seat that will work with your existing stroller.