Looking at the aging of Frost Giants in the MCU and the age of the actress playing Sylvie, it makes sense that she too is close to a thousand years old. Odin confirmed in Thor that Asgardians, who aren't actual immortals, age like humans do, just slower.
After a little math from Tumblr user nycstark, they deduced that, in human years, Loki would be around 16 "human" years old in the MCU. With that being the case, then perhaps Tom Holland would have been a more applicable casting choice for the teenage antihero.
Thor Odinson himself said he is around 1500 years old at the time of the events of Infinity War (2018), and MCU fandom wiki mentions Loki's year of birth as 965 AD, hence he would be 1055 years old at the time of his death in 2018. So, Thor is around 445 years older than Loki.
Canon. Loki and Thor are brothers, and Loki and Sylvie are variants of each other from alternative timelines. Due to the time-travel aspect of the Loki series, there are some variations in the canon/history of each character in this relationship.
The two trekked to a nearby town, and the two argued on the way, especially how Sylvie was a Variant but did not like to be called one, and also did not like to be called Loki. She then told him her name was Sylvie, and Loki told her that having an alias was not Loki-like.
Sylvie is an original character created for the MCU with inspiration taken from Lady Loki, a female form of the original Loki who debuted in Thor Vol. 2 #80 following the Ragnarok event, and Sylvie Lushton, the second iteration of the Enchantress introduced in Dark Reign: Young Avengers #1.
Superhuman Longevity: Like all Frost Giants, Loki aged far slower than humans. Despite being over 1,000 years old, he still maintains the physical appearance of a man in his prime. In Avengers: Infinity War, when Loki was killed by Thanos, he was 1,054 years old.
In the films, his most prominent relationships are with his family, notably his adoptive brother Thor (see: Thorki) and his adoptive mother, Queen Frigga. In his TV series, Loki and a female version of himself called Sylvie fall in love (see: Sylki) and their relationship becomes a prominent point of the show.
Superhuman Longevity: Loki has the capacity to live for thousands of years. Loki was a baby at the end of the last great war between the Asgardians and the Jotuns over a thousand years ago and is now in the physical appearance of a human male in the prime of life.
Asgardians age as humans do for the first 20-or-so years of their lives. Upon reaching early adulthood, they begin to age much more slowly. Asgardians possess different internal anatomy from humans, with their bones, tissue, and skin denser.
In one of Thor's movie loki mentioned that asguardian can live more than 5000 years and in the beginning of Thor: Dark world Odin mentioned that his father Bor fought the dark elves millenniums ago. Since it was mentioned that Thor is 1552 years old in the MCU, it would means that Odin was roughly 4000–5000 years old.
Despite their initial lack of trust, Loki and Sylvie developed a special bond and fell in love during the first season. Sylvie's actions in killing He Who Remains will have consequences that affect both her and Loki's personal journeys in the upcoming season.
Sylvie, born Loki Laufeydottir and also known as The Variant, is a character from the Marvel Cinematic Universe and the deuteragonist of the Disney+ series Loki. She is the Goddess of Mischief, a Variant of Loki who has been hunted by the Time Variance Authority most of her life and plots to destroy the organization.
While Steve Rogers gets the title of the oldest human avenger, Thor Odinson, as the mighty Asgardian God of Thunder, has a much longer life span than any of his Earth-born friends.
Yes Loki is dead, he got killed by Thanos in Avengers Infinity War (2018). But the Loki from the Loki series, is indeed Loki, but not the same Loki that died in Infinity War.
Asgardians aren't exactly immortal in the MCU, they just can live a very, very, very long time. Their average lifespan is about 5,000, which is an incredibly long time but most certainly isn't immortal.
Superhuman Longevity: Like all Asgardians, Odin was extremely long-lived, as he ages far slower than normal humans. During the last Great War between Asgard and Jotunheim, Odin was at least 18,000 years old, when he died, he was over 5,000 years old, if not older.
You asked two questions here, and I believe the second one, about Loki's identity, is quite well answered by the other Quorans here: Loki is a mortal Frost Giant, not actually an Asgardian; and even if he were Asgardian, he still wouldn't be immortal, despite humans believing that their Norse gods would be.
"Honestly, the way I always read that kiss is that her feelings were genuine and that it was a goodbye. Sylvie is sort of where our Loki was in Thor. She's driven by revenge, pain and anger, and that's what he's saying to her. He's like, “I've been where you are, and I just want you to be OK.
Loki, however, wanted to save the institution to protect everything from the onslaught of Kang variants He Who Remains promised was coming. Though, he also wanted to keep his friends Mobius, Casey and Hunter B-15 around him. Loki also fell in love with Sylvie, and arguably she loved him.
The TVA had taken Sylvie from Asgard as a child because she caused a Nexus Event that threatened the stability of the Sacred Timeline, meaning she had spent her entire life on the run from the omnipotent organization, though the exact nature of her Nexus Event wasn't actually revealed.
