In a large bowl, combine ground beef, panko breadcrumbs, egg, milk, onion, garlic, worcestershire sauce, salt, and pepper. Mix gently with your hands until just combined, being careful not to overmix.
Divide the mixture into 4 equal portions and shape each into a small oval loaf about 1 inch thick.
In a small bowl, stir together ketchup, brown sugar, and yellow mustard for the glaze.
Preheat the air fryer to 370°F (185°C). Place the mini meatloaves in the basket with space between each one.
Air fry for 12 minutes, then brush the tops generously with the glaze and cook for another 3 to 4 minutes until the internal temperature reaches 160°F (71°C) and the glaze is sticky and caramelized.
Let rest for 3 minutes before serving.