You should expect to have safe sex. Condoms are said to protect a person from unwanted pregnancies, Sexually Transmitted Infections and HIV. It is also used as a method of birth control. It is advised to wear condoms every time you have sex for maximum protection.
Don't worry about it, there is no age or anything so just go buy them and move on. Congrats on making a wise decision to protect yourself, many people do not do that so way to go on that! Always remember even with condoms there is a chance of the girl getting pregnant so best if she is also on birth control.