It is not a matter of "waking up your brain". Your brain never goes to sleep just because you are not in school. If you are active you are continuing to learn outside of school. For example, I know a guy (Registered Nurse) who was 67 when he earned his BSN and was also the valedictorian of his class. So, 34 is not an excuse for having problems in the classroom.
To be successful be sure to evaluate your reasons for taking these subjects. Are you doing so just because you feel you have no choice?? For instance you want to be a nurse because you have no choice. Or are you doing so because it is of interest to you and you have the abilities to apply the information?
Secondly evaluate your lifestyle. Is it conducive to your being successful academically? This includes work, family, and friends.
Last but not least, evaluate your study habits and your time management skills. If you are having trouble in any of these areas seek help. There should a department that specializes in tutors and other methods to achieve academic success on your college campus.