My oldest really started to get better after watching Pinball 101. Once he learned you can trap and pass, he got much more interested and his game improved. I think he was 7 or 8 when he first watched the video.
My youngest is 4 and she's just starting to get interested in the machines. She's more into "helping" me fix them up, but she's been playing split flipper with me lately. I think I may have to pop in the DVD for her soon.