Trusts can be customized to meet the specifics of the situation (wants and desires of the person setting it up -- your father in this case) even when they follow standard formats. There is no single answer to your question. You would have to look at the trust documents.
Speaking generically, trusts for minors are often set up to "expire" at ages of "majority" that are basically societal norms (18,19,21, or 25) but they can go on longer if the money is significant and/or the grantor (your father) thinks the beneficiary (you) might not be good with money at a standard age. For example, a trust might say "at age 25 if the beneficiary is married and has a 4 year degree, age 30 otherwise." Since it is unlikely that you have a trust worth big money ($1 million or more), I would guess yours is age 21.
Yes, the trustee is generally granted broad authority to use the money for the benefit of the beneficiary. This is particularly true of smaller trusts (under $100,000) and those entrusted to someone who will put their needs behind that of the beneficiary (mothers would fit into this category). The assumption in this case (and I would bet in yours) is that money is suppose to be "gone" by the time you turn 21 or 25. It is there to raise and care for you as a child (as if your father was paying child support) and if there is anything left over it is used to put you through college.
seek legal advice, but also is this other person really capable of doing such damage to you?... have they managed to ruin your record or credit, or some public documantation that employers have access to regarding your life? because truly these are really the most damaging, unless they managed to print an article or something about you in a major publication,... if so, then they have indeed defamed you. if not, then it's just gossipy hear-say, and this person is a hater and just let it go... or check to see if they have any dirt on them.. and use this in court if you can to show character profile of the person....