Everyone knows that 39 is not an actual age. There certainly are people walking the earth that have been alive for 39 years, but when someone says, "I'm 39," they're often being duplicitous. If a single guy is telling you he's 39, he is probably 41 and trying to cling to the last vestiges of his 30s to appear more eligible. The number of men with plastic surgery who swear they're 39 for years and years on end is growing, and if you don't believe me, take a trip to Los Angeles, California, and get back to me.
If you're actually 39, you might as well say you're 40. You're about to go from being the oldest person in their 30s to the youngest in their 40s. Isn't there an appeal to being a 40-year-old baby? If you're never going to turn 40, these 39 memes will stay 39 forever.