I have 2 trilogies I'd like to share. They're steampunk more or less.
The first one is the Airborne trilogy. (Airborne, Skybreaker, Starclimber)
It centers around Matt Cruse, who works on the airship, the Aurora, and also around Kate De Vries, who is a guest on the Aurora. Both of them are in their late teens
They meet on the airship during the first book, then the next 2 books are about their adventure's after Matt's stopped working on the Aurora.
It's a really good trilogy, perhaps even my favorite book series actually.
The second one is the Leviathan trilogy (Leviathan, Behemoth, Goliath).
Although Airborne may be considered steampunk, Leviathan definately show's more loyalty to the genre. This series is an alternate timeline of the first world war.
The 2 sides are renamed "Darwinists" and "Clankers". The Clankers being the German's and their allies, while the Darwinists are Britian and their's.
The Clanker's have massive machinery, and rely mainly on mechanical weapons.
The Darwinists have huge, fabricated beasts, that can substitute airships, seaships, and landships.
As far as the main characters, there's Alek, the son of the murdered Duke (the one who's death started the war), and Deryn, a girl in the military disguised as a boy. They're in their late teens as well.
The trilogy is about their journey's in the airship Leviathan, and how they end the war.