Even if it's just for fun you can learn as much as you want. Any secondary skills are always beneficial in business.
Good luck and have fun.
I don't believe the goal of working in the computing industry as a programmer is unrealistic at the age of 30+, if you enjoy programming you will learn quickly.
It's important to determine what part of the industry you want to be involved in - which you have done, due to the fact you want to stay within the finance sector it won't take you too long to become a proficient coder.
Try not to become overwhelmed with the notion of being 'too old' as your bound to fail with this mind set, so keep working through your books, reading and discussing within the forums and your be coding before you know it and your think to yourself, 'what was all the fuss about?'
btw, I'm 30, and do not consider myself to be 'old', chronologically I'm 30, but physically I feel 20 years 'young' :)
oh yes, I have also made the decision to learn Assembly and C :)