A while back, I was at a sporting event, holding my ticket and waiting for the race to begin, when a woman came up beside me and commented, "You know, the runner in lane one and lane two both have the same exact birthdate."
"Really?" I asked. "Same year, even?"
"Of course," she laughed, "it would be hardly notable if it weren't."
"And they aren't twin brothers or anything?"
"No." Her hair bounced as she shook her head. "Not even barely related. But what's really something is that the runner in lane three has the same birthday too. Day, month, and year."
"Wow!" I responded, "That is really impressive. Three of them, here, and they're all exactly the same age!"
"I didn't say that," the woman commented, with a smirk. "In fact, the second racer is three months older than the one in lane one."
"What? That doesn't make any sense at all. You said they had the same birthdate."
"Down to the year."
"But he's--" I gestured at the second lane of the track, "older than him."
"Yes!" The woman was grinning now. "And the third runner is three months older than he is! That's six months older than the first runner."
I crossed my arms. "Okay, clearly you're trying to mess with me here. I know how brainteasers work. What's the trick? Are we dealing with different calendars here? Or, like, the international date line? Or--"
The woman cut me off with a frown. "No, no calendar change, no Chinese New Year, no geographic shenanigans, no leap years, and!" she raised a finger, "no time-dilation absurdity here either. It's just the facts."
Fed up, I exclaimed, "Oh yeah!? I suppose the fourth one has the same birthday but is nine months older than the first, huh?!"
Snapping, "Don't be ridiculous," the woman turned on her heel and stalked away, leaving me to stare at the racetrack and the competitors and ponder. How could what the woman said be true?