seats aren't 'recalled' by age but manufacturers *do* have expiry dates for safety reasons. From the Car-seat.org FAQ http://www.car-safety.org/faq.html#Q25
"Q25: How many years can I use my carseat?
Many manufacturers now put "expiration" dates on their carseats. Six (6) years is the general recommendation. At most, 10 years is the accepted maximum lifetime of a carseat. The reasons for these limits involve possible degradation of the plastic shell and other parts, the possible loss/breakage of parts, and the fact that older seats will often not meet current government safety standards."
Here is a link you can use to check for recalls of a specific make/model of car seat: http://www.carseat.org/Recalls/recall.shtml
Would this other person be receptive to you purchasing a seat for her to use when she drives your son (assuming this is within your budget?). Perhaps she is using the old seat because she doesn't have resources to obtain a replacement?