Welcome Mary Mack and glad you joined Yorkie Talk. I personally do not have an older Yorkie and hopefully you will receive replies to your post with members who do have senior Yorkies.
I think it is such big hearted of you to rescue your senior Yorkie from the shelter. What is his name? If you'd like to, please post pictures of him as we all here "love the photo's"
I wish you the best with him - and I bet he is precious!
It may always be a mystery to his actual age but if his problems only consist of some bad teeth i would imagine your vet will take care of the problem and see no reason why he would suffer or pass away from it if his teeth problem is corrected. Regarding the eye, my friend has a Chi with a blind eye, he had to have it removed and the eye lids sewn but the Chi is happy as can be with his one eye and he is adorable.