Perhaps you will never have free time. Now is the time to learn. But Abba, I have my whole life to learn Torah. If you want to be able to learn your whole life, you must learn now. The Gemora explains that Hashem's ways are unlike those of mortal man.
Man can only create a vessel that is finite.
The more you fill it, the less room remains to add more. However, Hashem created a human being whose potential is infinite. The more he learns, the more he is able to learn. If you learn Torah and accustom yourself to listening when you are young, then you will be able to continue learning when you are older. However, if you do not learn in your youth, you will not be able to learn in your later years.