My last pooches who both passed away last summer.
Husky developed hypothyroid around age 7, degenerative disk disease was found at age 10. She ultimately passed away from cancer that we didn't find until 3 days before she passed. She was nearly 11.5.
My Malamute started have some neurological issues around age 6, very sporadic. The last year they became more frequent. We decided not to actively treat it. He was otherwise very healthy and active up until a week before he passed when he had a stifle injury and passed away about a week later from a stroke. He was 3 months shy of 13.
I almost lost Duke at 6 months due to a prostrate infection that was misdiagnosed and a SEVERE reaction to prednisone. I thought I was going to lose him; he couldn't go the bathroom and was hospitalized. I kept asking if the prednisone could be causing part of the problem and was told no. Several months later he had another infection and I put him on prednisone again. He had the same exact reaction - inability to go the bathroom and hospitalized. He no longer gets any type of steroid. And he was on heavy duty antibiotics for 2 months to clear up the prostrate infection plus a muscle relaxant to help him go for those 2 months. It scared me to death. I hope that is the worst I ever have to deal with for him until he reaches a very ripe old age...
Prednisone can be helpful, but there's a lot of bad side effects associated with it. I can also speak from personal experience having been on it for 20+years myself.
Talk to any golden retriever owner who has been in the breed for a long time and has had more than one dog in their life... they usually start holding their breaths by age 11 with their dogs. Doesn't mean the dogs will die at age 11, but that's usually the time when they start slowing down and it can become more difficult spot what to be worried about and what is a normal part of old age. It may be dogs sleeping deeper, being more reluctant to exercise, old age stuff going on with the eyes, dealing with goofy things like locking themselves in bathrooms more than usual, dealing with coats getting messed up, weights going up, fatty tumors suddenly popping up out of nowhere, etc...
Beyond that, I think it's helpful to give your dogs the best lives possible through their lives. Don't wait to spoil them until they are old.
I have quite a few dogs so hard to pick just one of those. These are just the dogs I lost to serious conditions I have had dogs that lived long normal lives but for the basis of your questions.
For goldens I have had four that Lost to serious health issues. two older ones that I took in when their owner passed away. They lived to 11 1/2 and 12 respectively they were both hit by cancer. Boots I lost him to bladder cancer at 8 and Sparkles I lost to a ruptured spleen at 11 /1/2.
I lost three of my shelties to cancer one at 10 one at 11 1/2 and one at 12. One of my shelties was lost at 9 to a severe reaction to amoxicillin another to a sudden cardiac arrest age 10.
My girl Katie ( Springer Spaniel) was extremely healthy all of her life until she bloated at age 10 and required a gastropexy to keep her stomach from rotating. She lived to age 14 1/2 after renal failure hit.
My beloved GR Yaichi was healthy most of her life. She developed a lipoma at age 7 which was aspirated and confirmed benign, however I do believe that at some point it became cancerous. I had to say good bye to her when she collapsed just after her 12th birthday, the lipoma burst several days later as I was nursing her. Collapse was due to hemangiosarcoma.
My beautiful girl Brisby ( now almost 4 years old) is the one that I have had early issues with; not life threatening however they do affect her quality of life. At age 2 1/2 she started leaking urine in her sleep. At first it was diagnosed as "spay incontinence", we have done some tests to determine if she has an ectopic ureter etc. I have a thread on this for anyone interested here It affects her quality of life as she is upset when she leaks, she gets urine scalding around her vulva and we are always on the watch for UTIs, which thankfully she has not manifested.
Brisby also ruptured her cruciate last summer at the age of 3. She has healed magnificently with conservative management with first rest/limited exercise, acupuncture, laser therapy on both stifles and supplements etc. This again was not life threatening, however did affect her QOL relative to keeping a young energetic dog from running, jumping etc. during a long healing process.
No serious health issues with my Champ until he got cancer (cardiac hemangio) at 13 years old. Only other thing to note: He did have pigmentary uveitis in one eye at 11, but it was very manageable with eyedrops and did not affect his quality of life at all, just fuzzy vision in that eye sometimes.
My sister's pug on the other hand was a nightmare with health issues. He was from a backyard breeder. He had couple bouts of serious aspiration pneumonia which were life threatening the last few years. He's blind with dementia at 12 years old.
We almost lost Benji twice when he was 3 1/2 months. He swolled a sock, which blocked his intestines, then he throw up the sock, causing his intestine to pull into its self, intussupception. He had to have an operation to fix his intestine, unfortunately 5 days later he had a reoccurance and required a second surgery. Thankfully he was a little fighter and ok s now doing well at 9 months.