How old is dustpelt?

As of the latest book (Omen of the stars: The fourth Apprentice), Dustpelt is not dead. You may have been confused with Ashfur who was is found dead at the end of the fith book of The Power of Three series. Squirrelflight found his body in the river by the Windclan border. I turns out Hollyleaf slit his throat and put him in the river in fear that he would expose her and her brothers' secret.