I think you can still learn it. Even though I'm not exactly "old" I spent ages typing with about 2-3 fingers only (reasonable WPM - 100+) but it terribly strained my fingers, even with a good mechanical keyboard and no RSI/wrist strength issues. I took about 4 months completely relearning how to type via www.keybr.com and typing game sites like www.10fastfingers.com and www.typeracer.com.
I now comfortable type around 110WPM average in a 'textbook' style of QWERTY typing. No longer feeling any sort of strain whatsoever. Give those websites a go :)