There are two main I think and actually I am experiencing it as well.
1. Once you hve finally decided to go back to school mainly to improve you knowledege most your well wishers actually appreciat it. And infact it is a mater appreciation.
2. You not be able to finance as openly to yourself, family and for your study as you would be before school. So just make sure that you have enough savings, or other mode of income, which suffice your tenure in school.
3. You have to be prepared for difference in thinking process, between you and your colleagues in class room. Yes, and actually the difference is created by the contrast in your way of thinking, developed by age, the way other in average age group of your collegues. It is not just study, but even the extra carricular activities also matters. And one have to work alot to get over the feeling of being more mature and more experienced while talking to fellow students. And only then you can get mixed up, but that too to some limits.