Onyx isn't a fan of the elevators, but he will get in them and sit next to me and look at me like "are we gunna die!" then once we are off all is well.
Practice makes perfect though, the first time in one was when he was 4 years old and he was scared. Now he just looks at me for reassurance and sits.
There is no age limit for the AKC CGC and some states only require this to do visits. In other states you must have your TDI and the dog (US) needs to be at least 12 months old to obtain this certification. In some states you can not work as a therapy dog unless you have obtained your TDI and work through an organization with insurance.
You can however start taking your pup to various places to get him used to strange sights and sounds. A couple great places to go are Petco and Petsmart (obvuiously), Home Depot and Lowes (lots of loud noises, strange smells and big carts), also I understand that Bass Pro Shop allows dogs.
You can also check with your local mall and ask if you can walk your pup up and down the mall, use the elevators, etc for therapy training
. You can get a bandanna or vest that says "Therapy Dog in Training." Most places are open to allowing dogs in training to do their thing as long as there is no food (grocery stores, restaurants, etc) out to contaminate. There are some restaurants that do allow dogs, I know a T-Bones here just opened their back deck to allowing dogs and even created a menu for them.
Good luck, if the dog enjoys it then do it. If your dog doesn't seem to enjoy it find something else they do enjoy. Therapy work is NOT for every dog.