Warren Buffett turned 90 this year. Berkshire Hathaway (NYSE:BRK.A, NYSE:BRK.B) vice chairman Charlie Munger is even older. Two older guys with two classes of stock. BRK.B stock is the more affordable of the two, at $291.28 a share versus $438,160. Source: Kent Sievers / Shutterstock.com Father Time is undefeated. Everything fades, everything ends. This may…