I am almost 29 years old, am I too old to go back to school? I have been out of high school for almost 10 yrs.?

I am a married mother of 4 girls. (12, 10, 4 & 2 years) I have been working full time since graduation and have always wanted to go back to school to become a teacher, but could never seem to find the time or money. Recently I was talking to my husband about being a stay at home mom and he agreed that I could quit my job, stay home and we would manage. I began to think about what I would do if something happend to him and i am left with 4 girls and no real way to support them. I have worked in child care for 3 years before and have been working the last 6 years for an attorney taking in traffic tickets. I can answer phones and make my way around a computer and fax machine but other then that I have no real skills. I have been thinking about going back to school full time to become a teacher but I am concerned about the costs and how long it will take. I am also feeling guilty about not being there for my girls, I know in the long run this will be better for all of us.