Replicants in the original movie had a 4-year time span.
Roy Batty was activated on January 8th, 2016. With the movie occurring in November 2019, his time was almost over. You almost wonder if he knew he was living his final days when he met the man who might be able to give him more time. As if he knew his heart was counting down its last beats. That he might not have two more months, but maybe only two more days when he killed Eldon Tyrell. About one or two days later, he meets Rick Deckard and explains as one slave to another what it's like to live as a slave.
Roy Batty knew he had to make every moment count to add more breaths, maybe even years, to his life.
Rick Deckard had no idea he was a replicant. When he and Rachael escaped, they had no idea that he would go onto live for decades. He probably suspected he had maybe a 4-year lifespan and counted back the years for which he was certain.
Gaffe (voiceover in Deckard's memory): It's too bad she won't live. But then again, who does?
Deckard (mental monologue): Gaffe had been there and let her live. Four years he figured. He was wrong. Tyrell told me Rachael was special. No termination date. I had no idea how long we would have together. Who does?
So how old was Rick Deckard in the original movie?