When I picked up some of my used equipment, I got three beer kits that were 9 years old. I posted the same question here and got a few mixed replies, but most said go for it except you obviously need new yeats.
So I actually started one of these 9 year old kits just this last Friday (with new yeast). I a newb so perhaps I didn't know better, but it really didn't look or smell any different than the first batch I made which was still within its expiry.
Obviously the taste test in a few weeks will be the final test - I'll post my results at that time.