All older horses will have little heath issues. So the skin cancer/eye thing wouldn't shock me as the last owners might not have been aware of it. Heck, I have a friend whose horse had a "bean" the size of a walnut in his penis and the friend never saw it until I pointed it out. The age thing would make my temper boil though!
I had a similar thing happen and the horse turned out to be outstanding for me, so you might just have to look past his age and love him anyway.
I went to buy an ex-broodmare who was supposed to be 11 years old and not in foal. She was to be my next trail horse. She ended up being 15 on her papers when we went to actually pick her up, but at that point I already agreed to buy her and didn't want to back out of the deal. I was sort of thinking of her as my next horse at that point. If they would have told me she was 15 I probably wouldn't have test rode her. I know that doesn't sound like a huge age difference, but I told myself I didn't want to look at anything over age 10 because I already had two oldies at the time.
So I bought her and love her to death. Although we couldn't get as much riding in that first year as she was also pregnant. Sigh! A very happy accident for me I guess. I love her baby (who is now a 2 yr old) although I sometimes wish I didn't have to go through the whole young-horse thing with manners and training. I only paid $500 for the mare and I probably have around $2500 already in training the foal, who just bucked me off and makes me want to tear my hair out.
You sometimes get little unexpected surprises when you buy a horse.
I also had a gelding (Paint) with cancer on his penis. He died at age 28 of unrelated causes. I had some luck with treating the lesions with blood root salve so you might want to ask your vet about that.