I have noticed some of my adult's legs are becoming scaly looking and some are even swelling.
would this due to age (they about 3-5 years old) or is there some else going on?
Pictures would help. Could be scaly leg mites. More info here, you can search for images.
Early on it will look like raised scales, when left untreated it can cause a lot of build up of gunk on the legs and feet, and can actually cause loss of toes. https://the-chicken-chick.com/scaly-leg-mites-in-chickens/
Thanks that does sound like it could be the problem. Do you think it would effect the laying of hens? Also; The article talks of treating the patient but do I also need to treat the coop?
It's a good idea to clean out and treat the coop also. The mites tend to stay on the birds, but they can migrate, so getting rid of them is important. I would clean out the coop, use a spray containing permethrin to treat all surfaces, and replace all bedding with new bedding. There are some sprays that are ready to use, and some you get in concentrate and mix with water to the correct dilution.