A "Is your guy like this?"
B "I think so. Or at least he pretends to."
A "Good. Hold onto him because guys like that get scooped up fast. Before you know it you're thirty and the good ones are all gone and then you have to wait untill they are divorced. But by then you'll be forty five."
Is the future simole used here colloquially? Shouldn't there be "But by then you will have been..."?
No. he will have celebrated his 45th birthday, he will have been 45 for x days/weeks/months, but he will still be 45.