I am 67 and fly a four-engine jet for a government agency, and I'm not the only one there in that age range. Why do I do it? Because I enjoy it, I am still capable and they value my experience. I have a nice airline retirement, so money isn't a motivating issue. The money is just icing on the cake. Being forced to walk away from what I enjoy just because a junior guy wants my seat is assinine.
How did you get to where you are today? Due to seniority, or due to superior skills, experience, training and/or luck? If the latter, then stay where you are as long as you want. If due to the former, then hold up your end of the deal and make way for the next guy.