Hey you're definitely not too old!
I've done a fair bit of reading around neuroscience and neurogenesis in particular and "too old" for learning doesn't really exist.
I've read recently quite a number of papers on sight-reading from differing disciplinary approaches and one thing they seem to agree on is facility of working, short- and long-term memories is absolutely central to the level of success in that task. Separately, it's established that the ability to encode new memories shows decline with age in both cross-sectional and longitudinal studies (quite distinct from neurodegenerative pathologies). It's challenging to understand how, at least with sight reading, you've managed to conclude there is no ageing-related limits to learning, unless you're thinking about molecular-level interventions to abate or retard the signs and symptoms of normal ageing?
I was strictly talking about learning as in general skill development and neurogenesis. I'm aware that sight reading is very different and never said learning doesn't slow down, of course it does. And yes, some things are impossible to learn as you grow. I wouldn't develop perfect pitch nor become natural at speaking mandarin even if I spend the next 70 years doing that daily.
Unfortunately, I never really looked into sight reading development during my academic studies (it was mostly brain trauma as that's what my research was based on and general concepts in skill development whether it was in humans or animals). Did you find any interesting studies? It would save me from going through systematic reviews (if any) or looking blindly throughout the literature for sight reading stuff. Would like to look through a couple articles myself.
While I don't know any people who took up piano at an old age, I've met a lot of people last year at my rowing club who took up rowing after retirement so just before the age of 70. I guarantee you that rowing technique is NOT easy to develop and while I was faster than the older group, I would get absolutely destroyed if anyone would compare my technique with theirs. Again, some have done it for 5+ years versus my half a year but my point is here that you can develop a skill at any age not that you'd develop it better/faster/more efficiently than someone younger. Also, there was an older team who took part in the Henley Royal Regatta if my memory serves me right, which is the highest level you can compete in the UK, if not in the world. Would they have been better if they started at 5-10-20-30-etc? Of course they would've been but again, the point is that it's possible not that it's the best thing to do.
I would become extremely sad if I even think that despite all the hard work I've been doing in the past two years there's hundreds/thousands of 5 year olds (prodigies excluded) who are much better than me simply because they started earlier. But then again, we only have one shot at this life thing so I'd rather learn as best as I can with what's in front of me and whenever I can than not learn at all.
Thanks for being more specific in your approach and sorry if my point was not specific enough
Having had a lesson today where I forgot to take my music glasses with me which meant sitting with my nose not far from the piano book and had a terrible memory lapse day I can so totally relate to this. I started at nearly 59 with very little musical knowledge and without meaning to belittle anyone else's achievements ( because i am in awe of some eg Peter who took his grade 5 today after such a short time)there definitely are things that don't come so easily as you age.
However i fully enjoy the journey and whilst i may not reach where i would have if i started earlier it is so much fun trying.
Also, absolutely no offence taken and although I'm relatively late, I understand my privilege and that being under 25 is different to being 70 or even 35!
Without meaning to be arrogant, I know that there's not many people that achieved 5 grades (well, will see once the results come in) in under 2 years and I highly doubt that anyone ever achieved it after 70 with ~ hour a day of practice in less than 2 years. I think there are the likes of Benjamin Grosvenor who did 8 grades in a year but 1) they're prodigies and 2) it was a a lot more than one hour a day and 3) they would've had lessons with Artistic Director of X/Y/Z conservatoire.