Easy to say, harder to practice. Money does not like to be spent in the right way, you have to practice extra discipline to be able to spend money as you plan. $100 a month is a good sum to DCA if you can, but as time goes on, try to see if you can DCA weekly, so you can have more within a shorter time.

Planning to DCA $100 monthly will only give you $1200 in btc at the end of the the year. You can get more if you create a weekly plan, or asides the DCA amount monthly, occasionally dump unplanned excess of cash that you will get from people like family and friends into your investment, since at your age, people know you are still financially dependent. That way you will be able to get more by the year's end.