Of course.
Is it a sin to not donate if you don’t really have much money?
As a minor, it is primarily your parents’ role to monetarily support the Church at this point. I see you are unbaptized and wanting to join the Church. If your parents are not religious or members of the Church, they are obviously not going to support the Church financially, and that would not be expected.
You should contribute what you believe you can, whether that is time, talent or treasure. At your age, you are capable of giving time and talent (such as serving at Mass, volunteering to help the less fortunate, spending time in prayer or adoration, etc.) if not treasure.
Each person is called to prayerfully discern what they are able to give. The Church teaches we are to support our local and the universal Church through prayerful stewardship. Time, talent, and treasure. The Church does not establish any specific giving criteria. We are to discern that for ourselves.
My advice is that you always be generous with time, talent, and treasure. If you can give a few coins, do so. If you can give a dollar, do so. When you get a job, prayerfully establish an amount you are going to give each week or month, and set that aside first from each paycheck.