That’s Oliver and I working on public access at 16 weeks. Not all dogs need to have the public access skills of a service dog but even pet dogs need to be exposed to new and different things at a young age.
Whether you are training a pet or a service dog start exposing them to new things early. Always control the situation as much as possible and keep it fun for the dog.
If you are training a service dog please take great care in how you socialize the dog to other animals and other people. Forget about the socialization group classes, they are completely opposite of what you need.