In J.R.R. Tolkien's The Lord of the Rings, Frodo and his Hobbit companions experienced a couple of dramatic adventures before even arriving at the Prancing Pony. Then, after one of the Nazgûl stabbed Frodo, the Elf-lord Glorfindel brought Frodo to Rivendell. In director Peter Jackson's adaptation, there were no adventures before the Prancing Pony (beyond a close encounter with a Black Rider), and Arwen took Frodo to the House of Elrond. After that, however, they formed the Fellowship of the Ring, and most of Tolkien and Jackson's work align perfectly.
One of the underappreciated ways that Jackson's adaptation aligned with Tolkien's source material was how accurately he represented the characters. One of the ways that Jackson did so was by making sure that almost everyone in the Fellowship was the same as they were in the books. With that said, here's a look at how old all nine members of the Fellowship were when they departed from Rivendell and how that affected their characters. The list runs in descending order of age.
Gandalf Was About 2,000 Years Old
The short answer is that Gandalf walked in Middle-earth for about 2,000 years before returning to the Valinor on Elven ships. However, there is a much longer answer. Like Sauron and the other Istari, Gandalf was a Maiar, an angelic spirit created by Eru at the beginning of time. Therefore, one has to calculate the age of creation itself to determine Gandalf's real age, which can be complicated.
The history of creation is divided into three parts: The Years of the Lamps, The Years of the Trees and The Years of the Sun (which comprise all three ages of Middle-earth). After a lot of math, and a conversion factor between Valian Years and Solar Years, a reasonable estimate puts Gandalf's age at about 55,000 years. That, however, doesn't factor in any time that passed before Arda was created. Either way, Gandalf was old and, thus, very wise.
Legolas Was 2,931 Years Old (in the Films)
Gandalf's age is complicated, but Legolas' age is even more difficult to pin down. Tolkien actually never specified an age for the bow-toting Silvan Elf. Moreover, there's conflicting evidence. Legolas called the other members of the Fellowship "children," indicating his advanced age. Still, he was never mentioned to have fought in The Last Alliance. So, his age could range from over 3,000 years old (considering his father was born in the First Age) to only a few hundred years old. Jackson simply picked a birth year for Legolas. According to the official movie guide for The Lord of the Rings, that year was TA (Third Age) 87, making Legolas 2,931 at the time of the War of the Ring.
Gimli Was 139 Years Old
Unlike Elves and Men, the Valar Aulë created the Dwarves. Because of that, Eru decreed that Dwarves would not have the same longevity as the Elves, but they also wouldn't taste the sting of Man's short life. That amounted to an average lifespan of between 200 and 300 years, although Dwalin lived to the ancient age of 340. During the time of the Fellowship, Gimli was 139 years old, which meant he was still relatively young, although he was beginning to feel middle age creeping on.
Aragorn Was 87 Years Old
Aragon's age can be deceptive. Although he looks like he would only be in his forties, Aragorn was actually 87 during the time of the Fellowship. Unlike the Elves, most Men in Middle-earth were cursed with short and feeble lives. However, the Valar granted the men of Númenor long lives because they assisted in defeating Morgoth. Númenoreans could live several hundred years, but because of Sauron's corruption and intermarrying, that gift began to fade. In all, Aragorn made it to the age of 210, so he was clearly still in his prime during the time of the Fellowship.
Frodo Was 50 Years Old
The Fellowship of the Ring opened with Bilbo and Frodo celebrating their birthdays. Bilbo was 111, and Frodo was 33. Hobbits considered 33 a coming-of-age year, so knowing that Frodo was 50 when he took the One Ring to Mordor meant that he was older than Jackson portrayed him in his films. Also, knowing that most Hobbits lived to be around 100 means that Frodo was around middle age, meaning he would have been more respectable than his Hobbit traveling companions.
Boromir Was 40 Years Old
Just like Aragorn, Boromir was granted the gift of a long life because of his noble (although diluted Númenorean) bloodline. However, Boromir was only 40 years old when he joined the Fellowship. That meant Boromir was less than half of Aragorn's age. That large age gap explained Boromir's often brash decisions, but it also accounted for his deference to Aragorn, who was the rightful heir to Gondor.
Samwise Gamgee Was 38 Years Old
Throughout The Lord of the Rings trilogy, Sam addressed Frodo as "Mister Frodo." That, however, didn't simply reflect his respect for the ringbearer -- it was deference as an employee and a younger Hobbit. Tolkien wrote Sam as 38 years old, making him 12 years younger than Frodo. On top of that, Sam was Frodo's gardener. Those two details explain why Sam called Frodo "Mister Frodo," even when Jackson wrote them to be closer in age. Regardless, he never really outgrew that servant mindset, and thanks to him, Frodo accomplished his quest.
Meridoc Brandybuck Was 36 Years Old
Only two years younger than Sam, Merry was 36 during the time of the Fellowship. That meant he was only three years past his coming-of-age birthday and barely an adult. Along with Pippin, he added some youthful vigor to the Fellowship, but he was more mature than the younger Took.
Peregrin Took Was 28 Years Old
Clearly meant to be a young troublemaker, Pippin was only 28 when they formed the Fellowship, which meant he hadn't even reached his coming-of-age birthday. In other words, Pippin was a jokester and always getting into trouble, as exemplified in the fireworks mishap at Bilbo's birthday party. However, it didn't end there, and he caused a number of problems as the Fellowship journeyed along.