I also did a gap year and felt really lonely but I didn't do much to counter it.
Jobs: look for agencies around your area - they will have temp jobs which are easier to get, and possibly office admin roles.
Volunteering: it's fine, it's expected the other volunteers will be older. It's nothing to be afraid of. There are so many opportunitiies out there.
Other goals: have you got your driving licence?
Don't let your thoughts bring you down. Make this moment count.