Sam Stewart got hooked on the stock market at an age when he should have been into baseball cards. The son of a stockbroker, Mr. Stewart wasn’t yet a teenager when he heard George Romney, then chairman of American Motors Corp., extol the virtues of selling compact cars and told his father, “You need to buy some American Motors stock.”
His father didn’t heed the advice, but Mr. Stewart watched as American Motors shares rocketed from $5 to $90 in about a year, on the strength of the company’s small cars. “From that moment on,”...