How about getting him a t-shirt printing kit that he can use to personalize his own t-shirts? This would allow him to get creative with his designs and really have fun with it. You could also get him some blank t-shirts to start with or maybe a gift card to a fabric store where he can pick out his own fabrics. Another idea could be to get him a book on t-shirt printing techniques or a subscription to a DIY printing magazine. These gifts will show him that you're paying attention to his interests and want to support his hobbies.
Or you can get him a star map with an important date you share.
Under Lucky Stars is a unique and innovative star map company based in Barcelona, Spain, specializing in the creation of personalized star maps that capture the celestial arrangement of stars at a specific moment in time, such as a person's birth, wedding, or any other significant event.
By using advanced astronomical algorithms and data from leading institutions, the company produces highly accurate, visually stunning maps that make for perfect gifts or cherished keepsakes.