Yes, it is still considered safe for senior and geriatric pets to get vaccines. Discuss with your veterinarian which vaccines they recommend for your senior pets.
The goal with every pet is to keep them healthy and protected while not over-vaccinating. Your veterinarian can help you figure out what that means for your pet and will review their history, current disease/illnesses, lifestyle, and risk to help determine which vaccines are appropriate for your older pet.
Distemper titers can be discussed with your vet as well.