Anyone can learn any instrument, but getting started is the hardest and most crucial part.  These characteristics tend to make beginning easier.

The Baritone/Euphonium is incredibly similar to the trombone, but doesn’t mind shorter arms.  Baritones require the same amount of air and air pressure to play as the trombone, but if a student is planning to transition to Tuba, they need a large lung capacity.  Baritone players can have a wide variety of mouth and lip shapes and sizes.  A strong frame can be important for carrying the instrument during marching, but isn’t a requirement unless the student is interested in transitioning from Baritone (baby Tuba) to Tuba.  Baritone players play both the melody and harmony often and usually have some of the fastest brass parts, so they may require more agile fingers.

Personality: Baritone players are usually more laid back than their trombone brethren, but they are also more accustomed to being the center of attention as there are usually fewer baritones on a given part than there are trombones.  Baritone players usually have a quiet confidence and mild demeanor – the more boisterous ones typically become Tuba players. 

Brass requires strong lungs and lips, but doesn't require fast fingers like a woodwind.  While I‘m not encouraging it, brass can take more of a beating than woodwinds, so younger or less responsible students can learn these instruments as they mature.  Brass instruments require good musical aptitude – they do not just play themselves if you push down the right buttons.  For this reason, brass players need confidence, strong lips, and good ears.  The ability to change their voice from high to low pitch and the ability to mimic someone’s speaking can be signs of a good beginning brass player.