I am here, read my post on my 70 mile run to get an idea of what a 50 year old can achieve :-
Thar and his EPIC run
I am 49 years old and I am fitter than I have ever been, I have been training at some level for 17 years. I have a club mates that did their personal best in their 50s. On the DNA level your body physical capabilities with training peak in your mid-twenties to mid-thirties, at 19 and 60 your capabilities should be equal if you have trained, after 60 then the aging process starts to catch up with you. It takes 12 years of proper running training to reach your bodies physical limits. So if you start now you will get better and better for a decade.
In endurance events you improve with age, the double world Ultra-distance running champion was 56 years old. The winner of the recent Tour of Spain was 42. A half Marathon is an endurance event.
You can train for a marathon in 3 months, so 12 months for a half is more than adequate, if you do train join a local club would be the best thing you could do, there will be people just starting out like you, while training you will have a great laugh and it won’t even feel like training. I would say train 3 times a week, two small runs in the week and a longer run at the weekend. As said once you can run 8 miles in training you will be able to run 13.1 miles in the race, whatever you run in training you can run 2 1/2 that on race day. For my Bob Graham round in training the biggest training run was a little over 30 miles.
As said start by walking for 10 minute then running for 5 minutes just for 30 minutes, build this up slowly by cutting back the time walking and increasing the running until you can run for 30 minutes. They normally say do not increase your weekly training by more than 10% per week, so you don’t get injured, but given the amount of time you have I would say that an increase of 5% would have you well fit enough to run it all. In fact if you do start training in 6 months you will be thinking about getting round in under 2 hours not if I can run all the way.
If you need any advice just PM me.
The only thing stopping you achieving this is the thing between your ears! Your 53 year old body is easily capable.
ATB
Tahr
Basil