Ya know, Mighty, you're not going to be alone unless you want to be.
You could end up with a guy who has younger kids. Or you could decide once your kids are gone to foster or adopt another.
When mine were all out of the house, I didn't have empty nest - I was kinda relieved not to have to make dinner every night, and supervise homework, and have time for ME. I was going through the divorce then.
But now, I do notice that sometimes, I'll read a story online about a needy teen and think "I could adopt them"! NOT actually something I want to do now, but I could see myself, when I'm semi-retired or retired, doing something like that.