The Simpsons as a stand-alone show aired in 1987 for the first time, and there have been 24 seasons so far. Since we don’t know Bart’s birthday, Bart Simpson would be 36 years old. However, they first appeared on the Tracy Ullman Show as a skit two years prior to getting their own show. As of 2013, if you count back to her show, Bart may even be 38 years old.
Lisa Simpson, Bart’s sister, is permanently eight years old in the show, so she would be 34 today, or 36 from the Tracy Ullman Show.
The youngest Simpson child, Maggie, is one year old in the show. She would be 27 or 29. The parents, Homer and Marge are 36 and 34. They would be 64 and 62.