When it came to romance, Karen Soltero adhered to two strict guidelines: “Don’t get involved with someone whose hair is nicer or longer than yours, and don’t date anyone you could have potentially given birth to.”

So in April 2018, when Ms. Soltero found herself chatting with Andres Peña, whose hair was twisted into a small knot atop his crown, she paused.

“I never trust a guy in a man bun,” said Ms. Soltero, 45, who works in sales in the Dallas office of Stampede, a global audio visual distributor based in Buffalo.

This was even before she learned that he was 16 years, 4 months younger than her.

But she had no chance to put her dating rules into action. The minute Mr. Peña, 28, who then worked for QA Systems, an audio visual integrator in Austin, Tex., spotted her he was smitten.