No, there should not be an age limit to buy condoms. Condoms provide safety for sexual contact, and that safety should not be denied based on age. Even if a teen is "too young" to be engaging in sexual activity, they may still do so, and denying them a condom is asinine.
I do not believe that there should be an age limit in order to buy condoms. The use of condoms is for the purpose of the prevention of pregnancy and the prevention of transmittal of sexually transmitted disease. I also believe that any one who would try to hinder another individual from those protections is not acting in the best interest of the community or mans basic need of health and welfare.