Many people are concerned that older dogs won't adapt to the idea of being crated at night or when left alone in the home, but crate training can be helpful for dogs and owners no matter what life stage it is started in. Some dogs will adapt quickly to crate training while shy, rescue dogs may need some encouragement to even enter a crate, but if you take it slow crate training an older dog should be no problem for any time of dog. Many older dogs will walk into a crate when led and can start being crated immediately. You can crate the dog at night or when you are gone but remember to also crate the dog randomly at times when you won't be leaving or will only be leaving for a few moments so that the dog doesn't begin to associate the crate with being alone.
You may want to crate the dog sometimes while you sit nearby and read or watch TV. Occasionally you should, out of the blue, lead the dog to the crate, ask him to go in, give him a treat, and then walk away without ever closing the door. This helps the dog understand that "crate" does not equal "caged". If you have the time to take crate training an older dog slower, you should. A dog will like the idea of crating better if he thinks it is HIS idea to sleep in the crate instead of yours. Evaluate whether you think your dog would like a private, cozy crate or one in the middle of the family and place the crate appropriately (i.e. A bedroom as opposed to a living room). Fill the crate with comfortable objects: a bed or blanket that the dog has slept on before. Add a few toys, and cover the crate all or part way with a sheet or cover. A covered crate feels less like a cage and more like a den- which is naturally appealing to a dog.
If your dog adult dog is shy or fearful, remove the crate door or use twist ties to secure the door open (a dog may be spooked if he bumps into the door or if it swings shut) and begin feeding meals near, then right in front of the door, then just inside the crate, and finally placing the bowl in and towards the back of the crate. Most fearful dogs will hate the crate if you force them inside, but if introduced slowly and without direct pressure (i.e. feeding inside but not forcing inside) they will begin to claim the space as their own willingly instead of being forced to, thus crate "training" themselves.