I think the age limit may be more about that individual. There are many who, later in life, have a different focus than the grind of adopting new technologies. ie: those who are older may want to use their wisdom more, serve in a leadership role.
However, I know a woman who is elderly who hacks PHP and does video editing for a number of small businesses. It is what she loves to do.
subject: Is there an age (upper) limit for an IT career?