Faizan,
"being a human being some restrictions are applicable to all humans within the frame work of a good human society."

I totally agree. In any good human society, there should be laws that ensure that people don't hurt each other.

"when the society liberalism reaches upto such a level that 99.9 percent girls lose their virgincy at the age of 15-17"

About 52% of American girls have had sex by the age of 17. The number is higher for boys; why aren't you worried about that?

"this relationship actually involves lust or unended materialistic desire"

I agree with you that 15-year-old are better off NOT having sex, but I don't see how it's the government's business if they choose to.