How do you make it work at this stage?

When you first get married, you and your spouse have all this time together, and you can be together any time you want.
Then you have kids. Mom is tired at the end of the day, baby is up at all hours, finding time to be together gets a little harder.
Then the kids get older, go to bed at 7 or 8, Mom and Dad can have some time together after the kids go to bed. (This was a good stage)
Now the kids are teenagers, they stay up until or after Mom and Dad are ready for bed. Mom and Dad can't shut the bedroom door (teenagers know what this means and it grosses them out). Mom and Dad are old and tired but still want time to be together....how do you make it work at this stage?