Yes, vertical configuration if ISSUED when holder is under 21. So if issued the day before their 21st birthday, they will have to live with a vertical license for one day short of 4 years even though they are legal drinking age.
DD was in that situation and as she rarely goes out and has an alcoholic beverage, it wasn't an issue normally. We were all in a bar at Phoenix Airport (we live in California) waiting for our flight home and they would not serve her because the bar rule was, "vertical license, no service" even if the birth date shows the holder is 21. She just shrugged her shoulders and we moved on. A few minutes later the server came back, asked to see her license again, and took it to the manager. Manager came back with her license and the drink she had ordered on the house. He said the vertical licences are designed to get warn servers that this person may not be 21, but to check the date to be sure.