Cliff Clavin was born in 1947 and is 39 years old in episode 6x10 "A Kiss Is Still a Kiss".
A faithful servant of the United States Postal Service, Cliff is often known to spout plenty of facts, the majority of which can usually be considered incorrect.
Cliff most likely inherited this trait from his Mother, Esther Claven. Cliff lived with his Mother for some time, until she accepted payment when their house was on property being bought up for development. When Esther moved to Florida, Cliff then moved into an apartment of his own in the Boston area.
Throughout the course of 'Cheers,' Cliff had two romantic run-ins. The first was with a woman on Halloween night in 1984. Though the woman (named Sharon O'Hare) met with Cliff shortly after this, the relationship did not last.
A few years later, Cliff was placed in charge of supervising a female Postal Employee named Margaret O'Keefe. A romance developed between the two, but after Margaret took her Postal Truck to make their romantic rendezvous, she found herself being fired from the service. She decided to go to Canada to be a part of their Postal Service, but Cliff declined to follow her.
Margaret did make 3 follow-up appearances, though in the end, she ended up staying in Canada, where she had become pregnant with another man's child.
Esther Claven would be down in Florida for a bit, visiting Cliff from time to time. Eventually, Esther ended up moving back to Boston, where she and Cliff once again shared living quarters. During the final season of 'Cheers,' Cliff considered putting Esther in a retirement home, but upon seeing how much the monthly fees were, he took her out of the home.
At the tail end of Cheers, Cliff received a promotion at work.
The final television appearance of Cliff Claven happened on a Season 9 episode of Frasier, titled "Cheerful Goodbyes." Frasier Crane and his family were visiting Boston for Frasier to give a lecture, but ran into Cliff at the airport, who assumed the family was there for his retirement party.
At this point in his life, Esther Claven was back living in Florida, and Cliff was planning to retire down there himself. However, he grew despondent that those of his friends in Boston didn't seem to care about him, leading him to confess these feelings to Frasier. Frasier requested the rest of the party guests (including Carla Tortelli), make it sound like they really cared about Cliff.
However, their positive musings caused Cliff to go back on his Florida retirement plans, and he decides to stay put in Boston.