Arlo Guthrie (see link at right), who I seem to be writing a lot about lately...he's 56 today.
Also, that diminutive devil-rocker Ronnie James Dio, who is 55. Dio's recordings with his eponymous band bore me to tears, but I've always kinda liked him as a vocalist with Blackmore's Rainbow and as a poor man's Ozzy with Black Sabbath. His vocal turn as "Froggy" in Deep Purple bassist Roger Glover's musical version of the children's book Butterfly Ball and Grasshopper Feast was surprisingly good and added a lot to a great record.
Rock on, Dio! Wooo!