Noctis Lucis Caelum is actually the youngest of the trio in 'Final Fantasy XV'! Gladiolus Amicitia and Ignis Scientia are both older, serving as his protectors and advisors. Gladio is the eldest, born in 1996 in the game's timeline, while Ignis is a year younger (1997). Noctis, the crown prince, is the baby of the group, born in 2002. Their age gap really shapes their dynamic—Gladio's the tough older brother type, Ignis is the meticulous caretaker, and Noctis gets to be the rebellious teen (with a kingdom's weight on his shoulders). I love how their relationships evolve throughout the story, especially when Noctis starts stepping into his role as king.
It's funny how age plays into their personalities too. Gladio's got that 'been through it all' confidence, Ignis is the responsible one always meal-prepping (bless him), and Noctis... well, he just wants to fish and nap. The game never outright states their ages in dialogue, but the lore books and Ultimania guides confirm it. Makes you appreciate how Square Enix designed their banter—there's this subtle hierarchy in how they tease each other.