Girls Bed Time Stories

What is the difference between girls aged: 8, 18, 28, 38, 48,
58, 68 and 78?

At 8 -
You take her to bed and tell her a story.

At 18 -
You tell her a story and take her to bed.

At 28 -
You don't need to tell her a story to take her to bed.

At 38 -
She tells you a story and takes you to bed.

At 48 -
You tell her a story to avoid going to bed.

At 58 -
You stay in bed to avoid her story.

At 68 -
If you take her to bed, that'll be a story!!

At 78 -
If you can get her out of bed, that's another story!!!