I've crate trained many mature foster dogs.
The best way is to make sure everything is positive about the crate. Make sure the crate is big enough for the dog to be able to lay down and turn around. Start feeding all meals in the crate. Put the food in the back of the crate, give a command ( I say "kennel up") and then let the dog eat the food without closing the crate. When the dog is comfortable going in and eating in the crate...start closing the crate door. Only give good things when the dog goes in the crate (save all of the treats and goodies for crate time)...such as stuffed Kongs or a marrow bone,etc.
Keep the dog in crate for short times while you are around...start with 5-10 minutes. Then work up to longer amounts and make a quick trip to the store,etc.
Everytime you want the dog to go in the crate, give the same command and throw a treat into the back of the crate.
Being that the dog is 5 years old, he may not need to be crated. It's good that he learns to be crate trained....but by that age he should be clean and non-destructive. Crating during the day while you are away would be good, at night he may be just as happy to sleep by your bed.
Start working on obedience training right away with him...and don't feel sorry for him because of his past.
Gina