Your little guy, Charlie is never too old to train! Classes are a good idea if you feel you would like guidance with his training. Its a good idea to fully research the trainer and get references and talk to other owners with small dogs that have used the particular class you might like to join.
I highly recommend Clicker Training if you have not heard of it. I went to it after training my first two dogs using traditional methods, its the only way I train now.
It is a very efficient training method and one I swear by and many members here have posted positive results with it. (If you do a search here, you will find many posts) It is very important to fully understand the methodology with it though, as a lot of people mistakenly think they just click and that makes the furbaby do things,
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Here is a link, they provide a training video, and a very nice little kit with flash cards and small book to get you going.
I think it was 19.99 when I got it a few years ago.
Karen Pryor Clickertraining
Another key is finding that one great training treat that they LOVE! We use Charlie Bears, very small, lightweight and they love them.
Charlee Bear Dog Treats | Products | Dogs love the taste, the crunch and the aroma of our treats