How many people do you know who regret being on contraceptives? They might regret the underage sex but the Gillick case is about being competant to access the contraceptives not conscent to the sex (which of course under law they cannot).
Accessing potentially permanent, life changing medical treatment that is still in it infancy and with regard to understanding the consequences is very hard even if you are a doctor never mind under 18, is not remotely comparable to accessing the pill.
So I have no idea if they are Gillick competant, but they damn well are not competant to assess research into the life-long consequences of a relatively new set of drugs and procedures.