It was written

When my older sister Rebecca was born, my mother was 29 years, 7 months, and 14 days. If our baby is born on time, Michelle will be 29 years, 6 months, and 13 days, or almost exactly 1 month younger. I was doing the math in my head and thought they were going to be the exact same age (would have been quite a coincidence), but was off by a month (it's still pretty close). I shared this with my sister, who told me that she was three weeks late, which puts her back on Michelle's timeframe. The reason I thought of it in the first place is because I use Mom & Rebecca's birthdays as one of the homework questions for my Excel class.

In an even greater coincidence, when Rebecca was born, my father was 30 years, 3 months, 18 days. If our child is born on time, I'll be 30 years, 3 months, 12 days, which is less than one week younger. Given the likelihood of the baby being late, there is a decent chance that my father and I will be the exact same age for the birthday of our first child. [Update: I now know that my first child, like his, will be a girl]

Finally, after running these numbers, I figured out that my father was 8 months & 5 days older than my mother. I am 8 months & 28 days older than Michelle, which is less than three weeks difference.