How long is a Sim year?

I play on Long and none of it ever adds up. One is called upon to suspend RL logic. It takes three days for a human Sim to fully gestate, which in RL might suggest one day equals a month in the Sim universe. But then we've got seasons. In RL a year is attached to four seasons. However, in the game, a Sim will age to the next level in far less than four season's worth of experience. It is the conundrum of the ages. I just wing it myself. Erik was 17 when he graduated early and went to Uni for three terms. At this rate, I surmise, he was all of 20 upon graduation. He now is married with the one child, an Infant, which suggests he's now 22 or will be soon. I tried to calculate it once, but I got lost along the way.