While there can be certain conditions before the beneficiary receives a gift, once that gift is transferred to the beneficiary, it is no longer under the control of the testator, their will or their executor. Once given to a beneficiary, the gift then belongs to the beneficiary who can do with it as they wish. If the gift is to be used in a particular way specified by the testator, that may be a moral issue for the beneficiary, not necessarily a legal one.
However, wills can specify the timing of the gift (when a beneficiary reaches a specified age). - Steve
In this country, that would be called a Trust. The gift would remain within a trust created by the testator or their will, and under the control of a Trustee whose job is to administer the trust as specified by the testator.