Alhumdulillah you are blessed that He has guided you in this age and Alhumdulillah now you understand the importance of prayers and fasts.
Yes it was the duty of your parents to teach you in your childhood but after the age of maturity it was your duty to read and understand the rulings as you did now because you were born in shia family where you have seen the people they are praying and fasting it was enough to understand the importance of prayers and fasts.
1) you have seen the people that praying and fasting it was knowledge.
2) there was not any delay in coming of guidance . It was negligence.
3) yes you have to pay qadha inshallah you will be able to pay the qadha I suggest you simple way at the time of fajr pray prayer of the day and one qadha same with other prayers
When you are not busy or in week end try to pray qadha for two days
Inshallah you will feel peace and satisfaction and inshallah Allah will help you in this great cause . My sincere prayers are with you.