My vet stops all vaccines except for rabies at age 10. They should have full immunity at that point. My Lila was due for a rabies vaccine at age 13 and I wanted to skip that too but my vet convinced me to do it because if something happened she would be able to quarantine at home. If the rabies vaccine was not current, she would have to be boarded somewhere for the quarantine period.
I personally, would not do a maintenance dental on a 13 year old, but I would address any more serious issues.
Bloodwork of course, and I would run a urinalysis. A palliative care vet told me that old dogs often have asymptomatic urinary tract infections that can become more serious if left untreated.
Congratulations on the upcoming milestone birthday!