As noted by the other answers, he was 195 years old at the time of The Hobbit. He was most likely aged down in the films for a variety of reasons. With Tolkien dwarves having an average life expectancy of 250 years, he was late middle aged to old.
The age of Bifur, Bofur, Bombur, Dori, Nori and Ori has been left unknown. However, we know that Balin was the eldest of the Dwarves after Thorin and that Fíli and Kíli were the youngest “by some fifty years”. This would put their age between 132 and 178 years at the time of the quest.
Thorin was born in T.A. 2746, presumably in the Lonely Mountain where his grandfather, Thrór, was King under the Mountain. Thorin was still a youngster (aged c. 24), by Dwarves' reckoning, when the dragon Smaug descended upon the mountain of Erebor in flames.
Fili and Kili, nephews of Thorin, are the youngest in the company of dwarves that visits Bilbo's house and sets out to reclaim their home in the Lonely Mountain. Of course, youngest, for dwarves, is always relative -- both of the brothers are about 80 years old.
To me, anyway, Bilbo seems younger than Thorin in the movie (as he is in the book). Also, their relationship is not really about relative age. Thorin's objection to Bilbo is not his youth it is his inexperience in adventuring and fighting and his seeming unsuitability for the burglar role.
The Life of Thorin Oakenshield | Tolkien Explained - Dwarves of Erebor
Is Thorin part elf?
TL;DR: Thorin is half-elf, and Fili and Kili are themselves both part elf and half-human. The two young dwarves represent the union of Elves, Men, and Dwarves that once existed before Dale fell, and which will rise again.
Legolas was portrayed by Orlando Bloom. In the "official movie guide" for The Lord of the Rings, a birthdate for Legolas is set to 87 of the Third Age. This would make him 2931 years old at the time of the War of the Ring. This date for Legolas' birth was made up by the movie writers.
Gimli is 139 during the events of The Lord of the Rings. Dwarves have an average lifespan of 250 years; thus, being young and strong, he was selected by Elrond to represent the Dwarves as part of Frodo's company.
If Smaug was born in the First Age, he should have been at least 6,212 years old at his death and he wouldn't have been "young and tender" at the falls of the two cities as he said he was.
Galadriel leaves Middle-earth in TA (Third Age) 3021 when she is around 8,000 years old. Given that the events of The Rings of Power take place before the Third Age, she's around 5,000 years old in the show. This is also corroborated by her birth date in Valinor of 1362 in the "Years of the Trees".
Gimli is the son of Glóin who is introduced in The Hobbit as a member of Thorin Oakenshield's company, also being one of his four third cousins. Thorin himself is a direct descendant of Durin I, even becoming the King of Durin's Folk in his lifetime.
Their deaths and Thorin's did not end Durin's line, although did end the branch which had Thror, Thrain, and Thorin Oakenshield. Thorin's cousin, Dain Ironfoot, became King after Thorin's death. Dain's son, Thorin Stonehelm, became King after Dain died in the Battle of Dale. The line continued on after that.
After the death of Thorin in the Battle of Five Armies, Dain becomes King under the Mountain. He redeems the Arkenstone from Bard with a fourteenth of the treasure, which is used to re-establish Dale. Over the next three years, Bard rebuilds the city of Dale and becomes its ruler.
Through the influence of the Ring, Gollum's life was extended far beyond that of other members of his clan. An average hobbit lifespan is over 100 years, but a span of 556 years separates Gollum's finding of the Ring and its destruction, by which time he was almost 600 years old.
After supper, Fíli and Kíli played small fiddles that they had brought in bags. The brothers were the youngest of the company by some 50 years, with Kíli being five years younger than his brother. Although not twins, the two brothers were inseparable throughout the adventure.
To that end, The Hobbit book stated that Smaug was a young dragon when he attacked Erebor. So, even though the "Smaug was a human" theory holds some water, all indication was that Smaug was born a dragon.
It is later revealed that Smaug's attack on Erebor was all part of Sauron's design, meaning that Smaug and Sauron were in league with each other. Smaug was considered one of the highlights of the second film of the series; several critics hailed him as cinema's greatest dragon.
Peter Jackson certainly makes the assertion in the theatrical and extended editions of the Hobbit movies that Smaug and Sauron are not only well aware of each other, but are planning to ally with each other. Smaug even seems to have detailed knowledge of Sauron's coming plans.
Gimli is not the last of the dwarves. This is a common misconception because Gimli is the only dwarf who gets a fair amount of coverage in the franchise. Lord of the Rings focuses its narrative primarily on the affairs of men, elves, and hobbits. Dwarves are a secluded race that lives in the mountains.
Tolkien provided few specifics about Treebeard's age, but he is estimated to be at least 11,000 years old, having tended to the trees before the Elves woke up in Middle-earth.
Lord of the Rings: Legolas Basically Married Gimli. Legolas and Gimli's relationship is strong in The Lord of the Rings, even though it wasn't explicitly romantic in Tolkien's source material. The members of the Fellowship in The Lord of the Rings forge an unbreakable bond while on their mission to destroy the One Ring ...
Loving Tauriel was a particularly harrowing event for Legolas. So much so, in fact, that he never shows any interest in romance ever again. He never even talks about romance in The Lord of The Rings trilogy.
In the extended version of the movie, Gandalf wants to interrogate Saruman, but Gríma Wormtongue (Brad Dourif) slays him before Gandalf gets the chance. In both the Lord of the Rings movies and the books, Saruman is definitely more than 1,000 years old.
