Here is how to change at will the size of your Start Menu.
Right-click on the Start menu, then choose properties.
Click Customize in the new window, increase or decrease the number of recent programs to display.
But if you want to reduce the maximum size of the start menu, you will not only reduce the number of recent programs to display, but also uncheck some checkboxes, for example: uncheck Help, remove links Help and Support. Or choose not to display the item to Documents.