lat year there was a sdn member worked at NASA and applied and got accepted into dental school. I believe that he has 4 children at the time. I don't think that 28 is old for dental school.
Regarding science classes, it varies so check with your school of choice, but I can give you a general list:
1. Calculus (1 year)
2. General Chemistry (1 yr)
3. Organic Chemistry (1 yr)
4. Biology-three introductory classes with lab. I took 1 introduction class, a botany and a zoology.
5. Statistics.
6. English Composition (1 yr)
To prepare for the DAT, I suggest that you take Physiology and Biochemistry.
To start, I suggest that you go to some dental office and ask to shadow for a few times, you should also have some dental experience, this can be volunteer and accumulate over the year.
I believe that other pre-dents will fill me in if I'm missing something here.
Best of luck
T