Dear Ambrose,  

It is not an absolute requirement, but if a person has fallen, it is necessary that he have picked himself up, be living chastely, and show by the control his passions that he is now able to live celibately.  

Some young people lose their virginity without knowing there is anything really wrong with it because 'that's what everyone does', only to realize afterwards (often with shame and horror) the truth. Others might have gone deliberately against their conscience. Both cases are different, but both require conversion, and conversion might come more easily to the first than to the second. After conversion both will require humility, effort to be faithful