From When We Were Young (#432) by Rabbi Avigdor Miller
When something is planted in our mind when we are young, it makes a very great difference. Don’t say that we will learn it some day later. Certainly it is better late than never; even at the end of our days. But, learning in our youth makes a very great difference.
When we learn young… what is it like? “It’s like writing with ink on fresh paper” (Avos). Ink on new paper takes and is more lasting. When we learn when we are an old man, it is like writing with ink on erased, worn out paper. It enters not only the paper. but it enters our neshama (soul). When the ink of Torah is inscribed on the tablet of our heart, we are changed from the inside out. A tremendous difference.
Any knowledge that we get is going to be like a seed
However, there is something else, another very great difference. Any thought that is planted in our mind is very important knowledge. Any knowledge that we get is going to be like a seed, it is going to have a root and a stem and it will produce fruit. What happens after a while? The fruits fall down again and new trees grow from them.
If we plant in our mind a fact that Hashem created the world out of nothing, He made the energy that causes chemicals to come into being. Therefore, we must these ideas into our head when we are young, we must place seeds. We will have new trees and the new trees will have new seeds and there will be a whole forest of trees and fruits in our mind as a result.
However, when other things come into our head, the world comes into our head, they also plant seeds. It is like a man that has weeds on his lawn and he does not take out the weeds. Next year, it is not just a few weeds. It is a forest of weeds. Like I said before, it is never too late to take these weeds out and try to plant because whatever we plant, is worthwhile.