I did a CELTA and am currently teaching in Vietnam - didn't actually end up teaching EFL in the end, but I'm in a similar job. Everything I'm about to say is based on my experience in Vietnam, so I don't know how it compares in other countries.
I don't think you're 'too old' as in your age is any reason why you couldn't do it, but realistically most people who do these courses and jobs abroad are going to be in their 20s or 30s, so it depends whether that's something that would bother you. If you're not interested in going to bars etc then you might not have much of a social life at work - again, depends whether you mind that. On the flip side though, people living overseas are generally very open to making new friends, and if you do enjoy that kind of thing then being older isn't likely to be an issue.
(Some countries do have age restrictions on EFL teacher visas, but I think early 50s would be below the cutoff for all or most - it's something you'd have to look into separately for each country you're considering.)
You also need to be realistic about your career prospects. If you don't have a 'proper' teaching qualification then you're not going to be hired by a day school, so you'll be working evenings and weekends teaching children additional classes on top of their normal school. It's a pretty chill job and the pay is enough to live on, but probably not the way you're used to in the UK, unless you work a LOT of hours. The days of making £40/hour just for being white a native speaker and showing up to class on time are (thankfully) long gone - everyone I know who does this kind of job lives in a tiny studio flat or a houseshare, mostly eats street food, only has occasional local holidays and isn't able to save that much. The lifestyle very much has a student feel, which I personally love, but it's not for everyone, and there isn't much opportunity for promotion unless you want to stay for years and become a manager or something. That's fine when you're young, but if you're used to having a proper career and thinking about saving for retirement etc then it might not be what you're hoping for.
The other thing I would say is, think very carefully about where you do the training. I did mine in Vietnam because I knew it was where I wanted to live, and it was invaluable in terms of making connections and getting an insight into where was good to work, where to avoid etc. My closest friends here are from my course and I would really, really have struggled if I'd just pitched up here and had to start a new job with no chance to meet people or settle in to the culture first. On the other hand, immigration is complicated - it was two months after qualifying before I could get a job due to visa restrictions, and six months before I was actually paid, again for bureaucratic immigration reasons. I spent about £5000 in that time including flights, accommodation, course fees, visa fees, having to keep leaving the country every 30 days because I wasn't technically a resident etc, and ended up having to borrow money from my family back home just to live. I had a very 'I'll work it all out when I get there' approach and completely underestimated how long everything would take - if I hadn't been in the lucky position of having family support available I would really have been fucked. There are millions of jobs available here and actually getting one was extremely easy, but I definitely wouldn't spend your last £1000 on the course assuming you'll be working soon afterwards.
All that said though, if you're not in a financially precarious position then go for it! In general I love my life here and so far it's been one of the best decisions I've ever made. Just be practical about it and make sure you do your research thoroughly first.