How does this work?

Whitney
I had my twins on Sunday May 24th. They are three weeks old today. Well they turned three weeks at 3:40 this morning. So next Sunday will be four weeks old. Does that make them a month old? It won't be the 24th though. It'll be the 21st. How does this work. Do I go by the weeks or by the 24th every month? I'm so confused.