Beamer’s default font size is 11 points. It is possible to set the default font size to any of 8, 9, 10, 11, 12, 14, 17, 20 on the \documentclass line. For instance, to set the default font to 14 points, do:
8, 9, 10, 11, 12, 14, 17, 20
\documentclass
\documentclass[14pt]{beamer}