Here are some small suggestions for you, I hope it will inspire you:
1. Go to a creative gift online store to customize a creative birthday gift for your friend. It is best to give something that reflects the days you spent together, such as a memoir. Write down all the happy things you can think of with your friends, and then find an online store to make a memoir and give it to him. You can send it by mail.
2. Whether your friend is working or going to school, you can give him a beautiful notebook as a birthday gift. Write down what you want to say to him and some words from his other friends in the notebook. This is more meaningful than anything else. I believe your friend will be moved.
3. Mail a book to your friend. Books are the best teachers. He must be very lonely when he is away from home. Books are his best friends. It is best to give him a book that can inspire him to live a good life. Give the best book to the best friend!
4. Give him a lighter. Whether he smokes or not, the lighter can be kept as a souvenir.
5. You can also choose birthday gifts according to your friend's hobbies. Buy him what he likes. You can buy it online and send it directly by mail, so you don't have to go out to look for it.