That will depend on what the "trust deed" says. The trust deed may be a will. Usually you would be entitled to a copy of it.

Have you asked the trustee? That is the obvious first step.

Sometimes the trustee has the power to advance money for those under the age of 18, for appropriate purposes.

Sometimes if the only thing preventing access is your age,and you are over 18, you may be entitled to require the trustee to give access anyway.

The trustee must act in the interests of the beneficiaries....as an interesting example of what a Court says about that, look at Hancock v Rhinehart (on Austlii website, Supreme Court, decision of Brereton J of about end May or early June 2015)...although it is 78 pages. I have a summary in about 4 pages if you want to email me.