Personalized White 21 on the Rocks Adult Sweatshirt. A large number 21 held up by three happy rocks and the text, on the rocks, is a funny birthday design for twenty-one year olds. Stay warm and stylish with this classic adult sweatshirt, perfect for everyday comfort. Crafted from soft, durable fabric, it features a relaxed fit for added coziness. Whether you’re lounging at home, running errands, or enjoying outdoor activities, this versatile sweatshirt is a wardrobe essential for any season.