I still whistle. I whistle when I'm happy, when I listen to music, and when I'm summoning the dog. I'll whistle while I work, and I'll continue to whistle until I physically can't make the sound anymore.
I've noticed that few people whistle anymore, and if I happen to be lightly whistling while walking around the grocery store, people give me the side eye like I just walked off an alien ship. Keep whistling and spread that cheer!