just in case anyone is confused

"I would have pegged him at 70" means "I would have identified him to be 70 years old," however due to modern slang it appears to be saying "I would have used a strap-on in a sexual act with him 30 years ago."

Allegedly, the older use of "peg" comes from using a wooden peg to make a door not close properly, so you can come back later and gain entry illicitly.

The modern version is conceptually similar but a very different experience.