All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
You are not sinful for not knowing that you are not allowed to drink or eat after dawn in Ramadan but you are obliged to make up the days you did not start your fasting at dawn. So, dear brother, you are obliged to take the initiative to make up for those years during which you missed to observe fasting properly so that you will be acquitted from your sin and meet Allaah with a complete and acceptable fast, Inshaa' Allaah. However, you are not obliged to make up the whole period consecutively without interruption.
May Allaah enable you to mention Him, be graceful to Him and worship Him as He should be worshipped.
Allaah Knows best.