I am still shooting loads sparked with primers my GRANDFATHER BOUGHT!!!! I have yet to have an issue with them!! BUT its all about how they where stored, not there age.
Recently some have had big problems with Remington primers. I have had about a half dozen cartons of rem primers for years with no problems. Al-tho I have never used the pistol primers from Remington.
The best advice I can offer is if you trust the handling of those primers, from that dealer, yes buy them. If not, pass on them.
CW