"I am fourteen years old."
Is です in this case necesary? I thought it is the polite version, and the sentence would work without, too
It is neccesary cause duolingo teaches you a polite form. Casual would be "da" but I dont recommend it unless you're talking to your friends
In casual speech, answering the question "how old are you" with just 十四さい is fine.
If you're wanting to make an independent statement about your age, then だ would be used. (Unless you're a girl, and you can say 十四さいよ instead)
they gave me the option to ですよ, then rejected my yo-ing. let me yo!!! if i am forced to lie about my age, let me at least be insistent on it!!!
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.
Small correction, Monica:
deru 》 demasu 出る》出ます
dekiru 》 dekimasu できる》できます