Your old man would surely love it if you can properly express your feelings for him, if you can actually tell that you are proud to be his son or his daughter. He will surely be glad to know that you actually care about him.
Every father wants to hear from his son or his daughter that he is loved and appreciated. There is something about hearing it firsthand that makes it a lot more better. Here are some old man birthday meme to show your love no matter how indirectly and show your old man that you also have some sense of humor, maybe he would laugh about it and thank you as well.
Try using it and maybe you can actually show him just how much you love him and how much you appreciate him and that you do have these feelings for him and you care about him a lot.