"I am fourteen years old."
No. Desu is a coppola that might be translated as "is" for some statemets although is a big simplification. Masu is a suffix used to make a polite verb using a verb stem i.e "deru" - dictionary form, used casually and "dekimasu" - polite form; "iru" - "to be" for animate things in dictionary form and "imasu" - polite form. Hope that helps. Sorry I dont have a japanese keybord on this device.