... or rather I could be 40 years old today but I'm not, thanks to a quirk in the way mathematicians round measurements to the nearest whole number. Thankyou mathematicians. And here's why. A line which is 39½cm long, when rounded to the nearest whole number, rounds up to 40cm. Likewise every measurement from 39½cm up to (but not including) 40½cm also rounds to 40cm. That's the way measurements normally work. Normally, but not always. Time doesn't work like that at all.
I am exactly 39½ years old today. If this were any other type of measurement then my 39½ would round up to 40 and I would be 40 years old today. But 39½ is a time measurement and doesn't follow the normal rules, so I'm not 40 today I'm still 39. I have been 39 years old since my 39th birthday last March, and will continue to be 39 until the day before my 40th birthday next March. One's age in years never rounds up, it always rounds down. It's more flattering that way, and I'm certainly not complaining.
Clock times round down too. It's half past twelve all the way from half past twelve and 0 seconds to half past twelve and 59 seconds. The time may be only one second short of 12:31, but we still say it's 12:30. But not all time measurements round down... some round up. Tomorrow is always a day away, even if that's in a lot less than 24 hours time. Next week is currently only four days away, not seven, next month is only three weeks away, not four, and next year is only four months away, not twelve. It's bloody complicated, time, and desperately inconsistent too. So maybe, when next March comes around, I can pretend not to be 40 after all by rounding my age to the nearest 25, downwards.