Early life. Thanos was born approximately 1,000 years ago on the planet Titan to A'Lars, along with his brother Eros.
Thor (about 1500 years old) in the MCU is a skilled Warrior who is apparently older than Thanos (about 1,000 years old).
Russo claims Thanos is around 1,000 years old, calling him to be "the Genghis Khan of the universe." The filmmakers could have chosen any reasonable age for the villain, but having Thanos be around 1,000 years old respects the larger canon of the comics, which, while vague, keeps him around this age.
Joe Russo, one of the directors of Avengers: Endgame, has confirmed that Thanos is around 1,000 years old.
Thanos is NOT immortal but extremely long lived (much like Asgardians, he does age). There is a difference between the original Titanian Eternals from which his mother Sui-San originated from and the immortal Earth Eternals (do NOT age, much like Olympians) from which his father Mentor/Alars originated from.
While Thanos is an Eternal and has the standard powers of super-strength, agility, regeneration, immortality, and more, Adam Warlock takes the upper hand. He can be killed, but he resurrects to be stronger every time.
Able to regenerate from any and all injuries, including death, Craig Hollis is unable to die and therefore dubs himself Mister Immortal, vowing to fight crime. With the two-dimensional Flatman, they form the Great Lakes Avengers in the Wisconsin area, despite lacking official Avengers sanction.
Directors Joe and Anthony Russo and writers Christopher Markus and Stephen McFeely provide the commentary, and they revealed that Thanos chose to wait because he had no idea about the location of the Soul Stone (via io9).
That villain is, of course, Kang the Conqueror, who's set to be the Avengers' next opponent in the upcoming Avengers: The Kang Dynasty. And while Thanos is certainly a hard act to follow, Kang may be a far greater threat than the Mad Titan ever was.
In the commentary, Joe Russo explained further: “The reason why [Thanos] has not gone after the stones before is because the minute he does, the forces of the universe are gonna line up against him. If he doesn't know where the Soul Stone is, then what is the point.”
Thanos is a mutant member of the race of superhumans known as the Titanian Eternals. The character possesses abilities common to the Eternals, but amplified to a higher degree through a combination of his mutant–Eternal heritage, bionic amplification, mysticism, and power bestowed by the abstract entity, Death.
Meanwhile, Groot was around four years old during the events of the Avengers: Infinity War and Endgame. Then, in The Holiday Special and Vol. 3, he is around five to six years old. If you count the time he was snapped as lifespan, in that case, he is around 11 years old in Guardians of the Galaxy Vol.
In the comics, Thanos is an Eternal, and one from a very important bloodline: His father, Al'ars, was the son of Kronos, who ruled the Eternals of Earth following a civil war that divided the original colony. Following his father's death, Al'ars traveled the universe as the Mentor.
Selene is the oldest known human mutant. Functionally immortal, her millennia-long life is attributed to her ability to drain the life essence from other beings to extend her own existence indefinitely.
Since the editor of the comic book decided to start the first issue with the story “The Human Torch”, Jim Hammond is popularly considered to be the first-ever Marvel superhero. Human Torch made the debut in the first story of the now-classic comic book Marvel Comics #1 (1939).
Thor is more or less immortal, granted the gift of everlasting life, thanks to his Asgardian genes and his special diet of the Apples of Idunn. In Avengers: Infinity War, Thor revealed that he was over 1500 years old.
3 Darkseid Is Thanos's Superior
The God of Evil has been fighting his wars for countless millennia and is one of the most powerful beings around. Few enemies have ever been able to beat him one on one and killing him is nigh impossible. Thanos is a fearsome enemy, but Darkseid is his superior in all forms.
1 Galactus Weakness Is His Hunger
Marvel has many powerful immortals, but few can match Galactus. The World Devourer controls the full might of the Power Cosmic, which gives him near complete control of energy and matter.
Thor. Blessed with the powers and long life of a god, Thor was undoubtedly the most powerful member of the initial version of the Avengers. Not only can he fly and transport between worlds, but he was also the only one capable of taking down Thanos, even after he had assembled all six Infinity Stones.
Instead of aliens, androids, and wizards, Thanos is afraid of aliens, Asgardians, and wizards. The theory posits Ego, Odin, and The Ancient One as three of Thanos' greatest fears, and he waited until all of them were dead to make his move.
"I think this is intrinsic to Tony's psychology, and because Tony started it all with Iron Man, he has a special connection to the threat that's facing him." This is how Thanos knows Tony will do whatever it takes to stop him. The Mad Titan sees too much of himself inside Stark... and that frightens him.
When Thanos got control over all six Infinity Stones, he became one of the most powerful beings in the Marvel Universe, though on his quest to obtain them, Thanos revealed that he was afraid to face the Hulk.
Hawkeye. On numerous occasions in the comics, Clint Barton has said he's just a regular guy with a bow and arrow. Unfortunately, his lack of power usually leads to him suffering from severe injuries regularly and has led to fans deeming him the weakest member of the Avengers.
The Scarlet Witch
Yes, the Scarlet Witch is the most powerful Avenger of all time. Even aside from the absolutely monstrous display of power that she showed in Doctor Strange in the Multiverse of Madness, Wanda Maximoff was always a major force to be reckoned with in the Marvel universe.