So your brother's a gear-head. He loves cars. He drags you to car shows. He spends countless weekend hours dicking around in the garage, "restoring" the old jalopies he buys all of the time. His apartment is decorated with giant posters featuring car porn (some of them even feature a scantily-clad woman who is disappointing her parents).
He'll say to you, "I don't understand why I can't get a girlfriend," and your eyes will get wild as you frantically gesture around to all of the car decor. Honestly, nothing says "I'm still a little boy" more than having a shrine to your favorite object in your home. Steer him towards something a little more sophisticated, like this Ford Mustang Watercolor (Starting at $60, Fab) from artist Alex Schmidt. The prints are bright, colorful, will look good framed on the wall, and still showcase his beloved autos (more car models are available, so he can pick out his favorite one).