The Mandalorian season 2, episode 5, "Chapter 13: The Jedi" brought Ahsoka Tano into live-action, and it's the oldest anyone's ever seen her. Everyone knows about Darth Vader and Luke Skywalker, and now even Rey Skywalker, but outside of the movies, perhaps the most famous Star Wars character is Ahsoka Tano. She was one of George Lucas and Dave Filoni's creations, and she was introduced into the franchise in the Clone Wars animated series as Anakin Skywalker's formidable apprentice.
Together, Ahsoka and Anakin fought the Sith, the Separatists, and their droid army for three years, in between the events of Star Wars: Episode II - Attack of the Clones and Star Wars: Episode III - Revenge of the Sith, until she unceremoniously left the Jedi Order shortly before the end of the Clone Wars. It was a shocking decision, but one that was necessary in order to maintain continuity with the films. She disappeared during Order 66 but thankfully returned in Star Wars Rebels, and now she's appeared in The Mandalorian.
Ahsoka Tano was born in 36 BBY, which means she was 14 years old when the Clone Wars began (when she first appeared on-screen) and 17 years old when they ended during Revenge of the Sith and immediately after the Siege of Mandalore (as shown in Clone Wars season 7). Since The Mandalorian season 1 takes place five years after Return of the Jedi and there's no clear indication of a major time jump in season 2, that means Ahsoka Tano is approximately 45 years old in "The Jedi", which is presumably set in 9 ABY.
If anything, Ahsoka Tano may be 46 years old, but judging by what's been shown in The Mandalorian season 2 so far, it's unlikely there's been a one-year (or longer) time jump. But there's certainly a big age-gap (28 years) between how old Ahsoka was in Clone Wars season 7 in mid-2020 and how old she is in The Mandalorian in late-2020. If viewers aren't familiar with Ahsoka Tano or are curious about what she was up to during the Age of the Empire, they can check out Star Wars Rebels, which shows Ahsoka in her 30s.
Star Wars Rebels took place in the five years leading up to A New Hope and the Battle of Yavin, which means Ahsoka was 31 years old in season 1 and 36 years old in season 4, but 40 years old in the series finale's prologue set sometime in the aftermath of the Battle of Endor. It's unclear whether or not The Mandalorian will explore Ahsoka's story any more, specifically covering her hunt for Grand Admiral Thrawn over the past five years, but it certainly looks like she hasn't lost her abilities as a Jedi (even if she isn't technically a Jedi now).