"Actually not all parents doesn't allow their teenage daughters or sons to have a relationship with others.
Those parents that doesn't agree that their teenage sons and daughters to have a girlfriend or boyfriend just wanted to protect them. It's for the sons and daughters own good.
The parents don't want them to have a bad future and nobody knows an accident may happen. What I mean about ""accident"" is teenage pregnancy. It is not good for the teenagers to be pregnant already. They might not able to took the pain to give birth and their health might be in danger.
There are many disadvantages in this kind of situation. The teenager might have encounter some problems in having a relationship and might do something not good for their health. Like taking their own lives just because of their partner.
It is also too early to have a girlfriend or boyfriend, if you are still a teenager. That's why you should study first. Don't rush things and think before you act.