Provisions such as you have encountered here are very common. A person who makes a will, a 'testator' , ( 'testatrix' if female)) may think that is not a good idea to let a young person get their hands on the money or property until that person is of an age at which the testator/testatrix thinks they'll to be responsible and sensible with it. So they say that the property is to go to X in trust until they are, say, 25 or 30 years old. On reaching that age the person gets the property.
Such a provision is not going to be changed by anyone.
In the meantime, you'll have to settle for being happy that you got something, even if you can't get your hands on it just yet. :)