In this case, '了' is a dynamic particle for emphasis, because there's a phrase '快要‘。 So generally speaking, those examples from 'bear234' is correct. I think you may wanna remember ’快要.....了‘ as a pattern. The reason why I noticed you is your profile, it says: 今年二十三岁了。This is a correct sentence without any grammar mistakes, but it's kinda childish to me. Of course we do say 我今年**岁了 in oral, and there will be a tone when you say it make it sounds natural. As you are writing, people can not see you directly so they don't know what's your tone and your mood. Actually I would say this sentence is more oral one, not a best statement in writing. I would say 今年23岁 if I were you. Hope this will help. :)