What is the ruling on starting prayer at the age of twenty-one, knowing the Prophet’s (peace be upon him) saying: "Command your children to pray at seven, beat them for it at ten, and separate them in their beds"?

The preponderant view is that one is not obligated to make up what was missed. Sincere repentance, remorse, seeking forgiveness, and diligent performance of supererogatory prayers suffice. However, the more cautious approach is to make them up, and this is the view of the majority.