I work with a guy who was raised Amish. He left the sect when he was about 20 and lives a normal American life, he’s about 50 years old now. He’s married with a couple of kids and a few years ago they hosted a German high school exchange student for a year. He could easily speak with her using his first language, Pennsylvania Dutch and her speaking German. She told him that his speech sounded to her like her grandparents speech.
I’m in the Lancaster PA area. I’ve been around Amish and Mennonites all my life.