I am 47 and the last time I tested max heart rate was whe I was rowing about 4 years ago. Man, it is painful! My suggestion would be to build you training zones off of Lactate threshold, basically the highest heart rate you can maintain for 20 minutes (after warming up), instead.
Joe Friel's book "the Cyclist's Training bible" is a good resource. I have also heard good things about Saly edwards book as mentioned above.