Strictly speaking the belts should be changed every 2 years (regardless of mileage). Personally I'm happy to push that to 3 years..........if your belts haven't been changed for 6 that's pushing it a bit too far
I would get them changed ASAP - if your dealer is going to be adjusting the old ones it won't be that much more to fit new.
I would also be slightly concerned if the dealer had not already recommended changing the belts if they are already 6 years old.