Why would it matter to you? Unless the adult class trains more often.
Still, to answer you, the only way for you to know is to talk to the teacher involved. Only they can tell you their policy for adult and kids classes.
That depends on the school. In my school you would be provided that your attention span is good and that you are able to stay focused when training and don't need the teacher to constantly breathe down your neck to keep you motivated, training and paying attention and that you can follow instructions and make corrections the way the teacher explains them, that you show a good amount of respect and that you train hard. Being able to train in a mature manner is important that you do not hold back others in the class. Remember it is not about you only but that the others also pay tuition and are entitled to receive constructive training. If a student can not keep the pace in an adult class then maybe a youth class may be more suited until the student is mature enough and has enough basics to join the adult class for the mutual benefit of all. If a class is too fast paced for you you will get frustrated and then it is not fun for you either. So don't make it a pride thing. Make it where you will fit in best and will learn the most.