My grandson, there is no standard age for a boy to be able to make a girl pregnant or for a girl to get pregnant. It all depends on the individual physical development and when their hormones will be ready. But generally boys do get the ability to make somebody pregnant when they hit puberty and this applies as well to girls, for they get pregnant when they hit puberty.
Boys hit puberty at the average age of 14, and they finish getting the signs of puberty at the age average age of 18. This means some boys can get puberty signs before the age of 14 as there are others who finish getting puberty signs above the age of 18. Girls on other hand hit puberty earlier, compared with boys. In general, they witness puberty signs at the average age of 12 and they finish getting these around the age of 18. This means some girls can get the signs even before they are 12, and some finish getting the signs above the age of 18.
However, if and when you decide to have sex make sure you and your partner are emotionally ready for it. And make sure you are taking all precautionary measures to protect yourself from unplanned pregnancies and STIs.