The minimum age to buy stocks independently is the age of majority, which is between 18 and 21, depending on the state, according to The Motley Fool. However, a minor can open a "custodial account" with a parent who authorizes the minor's participation.
On a custodial stock account, a minor is able to enter buy and sell transactions on stocks in the same way as an adult trader. An informal alternative is for a minor to simply pay cash to a parent who places trades on an account, according to The Motley Fool. With this approach, the key is to record share ownership and to account for price gains or losses.