Wait a minute… checks maths
Age is a personal piece of information, but you can’t be old enough to spend money for your dad’s birthday. Even if he had you at 18 and you’re almost an adult.
If you feel like your dad has everything he needs, you might be right, and he’s a lucky bastard to have you. Keep your money and write him a letter.
Well that’s great! Happy belated birthday. My comment might have been a bit rude in its wording, sorry, but I insist. As a father of 2, only a couple of years older than yours, I think any sign of mutual understanding of the incredible power of parenthood surpasses a material gift.