Here's a great quote from Clayton he said on a podcast:
"As we get older, we don’t want to fall, which means we don’t learn. Only when you make a mistake can you learn from it. But if you’re not making any mistakes you’re just going to plateau out and you’re eventually going to get worse.”
- Clayton Nienaber
I don't think you can ever be too old or bad to get better at surfing. This is particularly true for those who do not have a solid technical foundation. For whatever reason the surf culture rejects learning technique, coaching, etc.. That's fine, most are happy being intermediate as ignorance is bliss. I regret getting caught in that mentality myself now though. I have more fun surfing when trying to get better and setting goals, and have decided recently to focus on it.
BTW, I just rejoined Martin Dunn's site and he has updated everything and added a ton of new stuff. I find his teaching approach vey useful and the best out there. Also Noel Salas has a patreon page now where he has surfing technique videos with skating drills. Also good.
Next step for me is to get videos of my bad technique and cry. I'll eventually probably send in a video to someone for coaching when I get stuck on something.