L was initially 24 years old at his first appearance in Season 1 of Death Note, and he later turned 25 during the course of the series, before his eventual demise.
L's Age Progression in Season 1
L, whose full name is L Lawliet, makes his initial appearance early in the Death Note series as the enigmatic detective tasked with catching Kira. According to character information, his birthday is October 31, 1979.
- Initial Appearance: L first appears on December 5, 2003, to the public and the Task Force. At this time, having passed his birthday for that year, he was already 24 years old.
- Turning 25: During the events commonly associated with Season 1, L reaches his 25th birthday on October 31, 2004. He remains 25 until his death on November 5, 2004, which occurs in Episode 25, typically considered the conclusion of the first major arc or "Season 1" of the anime.
Therefore, for the majority of his active investigation in Season 1, L was 24, and then briefly 25 before his death.
To clarify his age timeline:
| Event | Date | L's Age |
|---|---|---|
| L's Birthday | October 31, 1979 | N/A |
| First Appearance in Season 1 | December 5, 2003 | 24 |
| Turns 25 | October 31, 2004 | 25 |
| Death (within Season 1) | November 5, 2004 | 25 |
This timeline shows that L was 24 years old at the beginning of his involvement in the Kira case in Season 1 and subsequently turned 25 during the critical moments leading up to his death, which marked the end of the initial arc.
