Too old to be realistic in her new role in The Middle?

NO! There are many women who are choosing to have children later in life for one reason or another. Or the youngest child who comes along later in life is a nice surprise, though unplanned. Happens all the time. I think her character represents many women. My own grandmother had her last child at age 47! Besides, until you posed the question, it never occurred to me to think she was too old.