You won't believe how old Reese Witherspoon's daughter is now

Prepare for a reality check!

In a couple of months, Reese Witherspoon's daughter will be an ADULT.

Reese gave birth in September, 1999 at the age of 23 to Ava.

In a recent interview with ET, she relayed just how quickly time has flown by:

“It’s so weird. I can’t believe she’s 18. But she’s great, and we did it together. I feel like we grew up together, it’s great.”