Only two Slayers were ever known to be older than 25 with a Mark. Yoriichi lived till old age, likely due to him having been born with the mark and thereby avoiding the curse altogether. Gyomei on the other hand did not activate his Mark until he was already older than 25.
Unlike all other Marks users in his era, Yoriichi was able to defy fate and lived to about 85 years of age.
Demon Slayers who have awakened the Demon Slayer Mark are said to die upon reaching the age of 25. Kokushibō speculated this to be because the mark exchanged the life span of its user for power. There are ways to avoid death through the curse, as shown by Yoriichi and Kokushibō.
Fans of the series, who know that Yoriichi passed away a long time ago, wondered who the person was that resembled the legendary swordsman who nearly defeated Muzan all by himself. It was soon revealed that Tanjiro wasn't looking at an actual person at all. In fact, he was looking at a mechanical doll.
In the Demon Slayer manga's final chapter, Yoriichi and his family have been reincarnated and are seen in the deep background of a panel as Tanjiro's own descendants head to school.
2) Kokushibo
This Upper Moon 1 went up against Yoriichi and managed to make it out alive. He gave everything he had but still managed to receive a heavy slash. Just before he received the second cut, Yoriichi died when he attempted to recover from the first move.
When Yoriichi died, he died crying for his older brother who turned into a demon. He cried because he couldn't accomplish anything he was supposed to in his life. And then, Tsugikuni Yoriichi was reborn as Tanjiro Kamado, an omega prime.
Yoriichi lived till old age, likely due to him having been born with the mark and thereby avoiding the curse altogether. Gyomei on the other hand did not activate his Mark until he was already older than 25. It was speculated that when he awoke his Mark during battle that he would likely die within hours.
Yoriichi lived until around 85 years, so: 1432 + 85 = 1517, exactly 400 years prior to when Kokushibo remembered and died.
When Yoriichi moved forward to kill him, Muzan used the remains of whatever power he had left and divided his body in a powerful burst. Though Yoriichi was able to destroy nearly all the fragments, the pieces he missed escaped and allowed Muzan to regenerate again.
Unfortunately, manifesting his Mark in the battle against Akaza also doomed Giyu to die by his 25th birthday, taking the air out of the sils of his survival.
As the battle reached its climax, Tanjiro was able to knock the doll's head off and discovered that the mechanical body contained a mysterious sword. Fans of the manga will recognize this sword as the one carried by Yoriichi Tsugikuni himself.
Yoriichi would be able to defeat every single Hashira on this list without breaking a sweat. Such was his reputation and skill in swordsmanship.
During episode three we learned that the Yoriichi Type Zero was built by Kontetsu's ancestors more than 300 years ago, during the Sengoku era.
Yoriichi is the progenitor of Breathing Styles, born with a demon slayer mark, which means he never had to go under special training to awaken it. He was the user of the Sun Breathing Style and the first swordsman to ever use the breathing style.
It was because after being shown his overwhelming power, Muzan avoided him as best as he could. He didn't have another chance to kill him.
Yoriichi was undoubtedly a prodigy of the sword which has not been seen since his time alive. Truly, there is no one who can best or even match him in terms of breathing style and swordsmanship mastery.
After that Sumiyoshi urged Yoriichi to return someday but before he left Yoriichi gave his earrings to Sumiyoshi making it clear that he would never return.
Tanjiro and his father look extremely similar to each other. Fans think that Tanjiro was related to the legendary swordsman since he had the same earrings, and their appearances are similar as well. However, Tanjiro is not a descendant of Yoriichi Tsukiguni.
Tanjirou, Sanemi and Giyuu probably all died by age 25. This has nothing to do with the eradication of demons.
Instantly, Yoriichi's ability, the power to see the transparent world with his heightened perception, enables him to see through Muzan and discover that the powerful demon possesses five brains and seven hearts that can move at will within his body.
As Yoriichi spoke of his regret for coming to his house to eat free food, Sumiyoshi tries to remind him that he had saved him and his family, and they owe him great gratitude for it.
Besides Sun Breathing, Yoriichi possessed a wide range of traits and abilities common with the strongest demon slayers in the series. For example, he was born with the demon slayer mark, greatly enhancing his physical capabilities.
He was a man who received no formal training in combat and managed to take down a bear with a short axe. To sum things up, Tanjuro was one of the strongest characters aside from Yoriichi, given that he was able to access the Selfless State for hours on end.