All the known scholars of Islam - Ibn Taymiyyah, al-Bukhaaree, Al-Imaam Ahmad, Ibn Hajar, etc, were not born as scholars.
In other words, they were born ignorant just as you and me were so born.
Allaah the Mighty said:
وَاللَّهُ أَخرَجَكُم مِن بُطونِ أُمَّهاتِكُم لا تَعلَمونَ شَيئًا وَجَعَلَ لَكُمُ السَّمعَ وَالأَبصارَ وَالأَفئِدَةَ لَعَلَّكُم تَشكُرونَ
And Allah has brought you out from the wombs of your mothers while you know nothing. And He gave you hearing, sight, and hearts that you might give thanks (to Allah).
Thus it was by the Mercy of Allaah those people became what they became, then personal efforts made by them under this Mercy. They really made serious efforts and Allaah the Bountiful Lord blessed the efforts.
So never underrate yourself. Never say you can never have knowledge. Don't say you are dull. Don't say people have gone.
Rise and learn.
So far you have your intellect with you. You are healthy. You can move about. Then you have no excuse not to learn.
Never lose hope even when you are not so that sharp in memory. When you don't understand things quickly. When you forget things quickly. Make efforts against that and overcome those weaknesses.
Purify your intention and go after knowledge.
Create a sense of self-discipline in yourself. Make good use of your time. Avoid frivolitiies. Make less friends. Go after scholars. Buy books. Be in company of knowledge seekers.
Be consistent in learning. Don't be hasty.
Take Qur'aan memorization as an instance, by repeating a single verse over and over you will master it, and so on. The same thing goes for hadeeth.
Just continue to make efforts no matter how little.
Al-Imaam al-Bukhaaree - rahimahullaah - was asked what was the antidote to forgetfulness, he said:
مداومة النظر في الكتب
"Constantly looking in the books".
Lastly, shunning sins is one of the ways of retaining knowledge.
Al-Imaam Ash-Shaafi'ee - rahimahullaah - said:
شكوت إلى وكيع سوء حفظي #
فأرشدني إلى ترك المعاصي
وقال اعلم بأن العلم نور #
ونور الله لا يؤتاه عاصي
"I complained to Wakee about my poor memory#
So he guided me to shunning sins
He said know that knowledge is light#
And Light of Allaah is not granted a sinner."