Will David Mitchell is blessed with uncommon energy. At 73 years of age, last Good Friday, he spent the afternoon running all over a soccer field, showing people how to fly 4-line stunt kites. After more than three hours, they were winding up their lines, seeking park benches and asking him to go home. He was certain he'd be sore the next day, but wasn't. The next day, they repeated the playful session. The third day, again, he was not a bit sore and was playing the saxophone as usual in his church's worship band. He attributes this energy and fitness to the minerals he consumes, quipping that...