I had written out a reply and it disappeared... This may show up twice...
Stanley (13) had a hyperthyroid scare last year. The vet thought he had it and we discussed options while we waited on the T4 numbers to come back (thankfully, he did not have it).
You mention surgery and medication. My vet encouraged a third option. I believe it was called Radioactive Iodine Injection/Treatment (or something of that nature). Is the most effective and highest success rate of all three methods. 90-something percent effective rate -- one treatment generally equals total fix of the problem. However, it is also the most expensive. I believe it runs about $1,000 (to give you an idea, although, regions vary). The cat basically has a shot in the thyroid and then sits for about 5 days at the clinic to be watched and primarily because it is radioactive (safety laws, etc.)
Stanley was younger, it may or may not be adviseable for your cat. If you don't feel your cat will do well away for a week, another concern.
But, it is more effective than the surgery, as my vet explained. Also less invasive, etc. Stanley is/was relatively young and she said medicating for years can be costly and a hassle. Surgery isn't 100%. This third option was quick, fairly easy for the cat, and about 100% cure rate.
However, with your cat being older, you have other concerns to weigh in. I'd discuss with your vet...
You can also find more, as I did, by searching on the web for "Hyperactive thyroid cats" or other similar phrases and the three options pop up pretty commonly in discussions.
Note: My Uncle successfully medicated his Siamese for years for thyroid problems. She passed away at the age of 18, but he had treated her for years...
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Tammy
