How old are Ben and Olivia?

Today's comic was created when Daniel wasn't yet certain how old his characters were. In fact, the first few months were uneven in terms of the references to hearing aids and other things that make Ben seem like he is in his late seventies, and yet Olivia is very active in her exercise classes. Later on, the Hatleys grew into the more contemporary figures they are now, although as Daniel's parents (the real-life influence behind the comic strip) grow older and less active, he has to be careful to remember that Ben and Olivia nevertheless stay at their age of early 60s.