They can't learn a new language.
They can't learn a new skill.
They are too ignorant to start a business project.
Because they're old.
This notion that only young people can be successful and follow their dreams comes from overemphasizing abilities of the physical body. When the body gets older, for many people it seems that the value of the person diminishes. For a senior person who buys into this myth, the meaning of life diminishes as well.
But following your dreams has nothing to do with what your body can or cannot do and has everything to do with the bravery of the mind.
Bravery is a skill which can be taught and learned whether you are 7 or 97.
Leap (in your mind, of course).