Old age or ill ?

The last couple of days my R.C.R.I.R. roo has not been acting quite right. Last one out of coop instead for first. Not hanging with the girls. Going to roost before everyone else. etc. No other sights of illness except a bit of loose droppings. He is about 3 yr. old. How long to R.I.R. birds live ? Our weather has not been extremely cold but we have had rain for days and days. Despite spotless water bowls the birds drink out of the puddles in the barn yard, (horse poo and yuck). I wormed w/ Valbazen end of Jan. Over a year ago I lost 12 birds(I got from a hobby farm in Ga.) to Lymphoid Lucosis ? Any ideas or suggestions ? I really hate to lose this guy. He is a very sweet roo just about perfect in every way. Thanks ! p.s. I hatched Randy so he was NOT vac. for Merck's. I was uneducated about it at that time. But there has been no fowl in or out of here except wild ones.