The older people get, the more lucid, luminous and powerful they can become. If this is not what we typically see, it is because human beings are so used to identifying with their physical body that they submit passively to all its trials and tribulations.
However, for a truly spiritual person, it is just the opposite: their thinking becomes increasingly vital and active, for they have learned to free themselves from the constraints of the physical plane and identify with the spirit.
The spirit is all-powerful, the spirit is immortal, the spirit is omniscient, and when you identify with it, matter no longer has the same hold on you.
Our physical body must obey the laws of matter, but the spirit is under no such obligation.
That is why age is no disadvantage for a spiritual person; on the contrary, their thinking becomes freer and more active on the subtle planes.