Well, I would and have definitely done dentals on my senior high risk dogs.
I my cases I had dentals done on an 8 year and a 10 year old, both great danes, so that is very old for their breeds. The second one lived to be 13 and only died due to degenerative myleopathy.
We do dentals on senior dogs very frequently, and as long as they are done properly with lots of supervision and having had all the proper pre-anesthetic work done, your risks are VERY minimal. However having extreme gingivitis creating open pathways for bacteria to enter the blood stream in a senior dog who often have weaker liver and kidneys to me. Is a MUCH bigger risk to shortening your dogs life than the anesthetics.
We have often had clients who were questioning how "old" their dogs were, and if there was any point in doing the dental since their dogs seemed "on the way out" anyway, come in exclaiming their dogs were suddenly way more active again and eating so much better.
If you are worried, maybe get a second oppion from another vet, but don't tell them your concerns. If they too immediately point out teeth, I'd for sure consider it... Just my 2 cents for what they're worth
I'm sure you'll make the right decision, EITHER way you go