My gelding, Specs, is 12 years old and all I've ridden him in is an O-ring snaffle (except at shows, I usually use a tom thumb because that's the only curb I have around, and I have to show in a curb because its 4H rules.)...
He has lots of problems with the Tom Thumb, (like head throwing/general uncomfortableness), and I kind of wanted to move out of the O-ring into a curb. Not because he's out of hand, but because I think he's mature enough to be
Neck rein well
Plow rein when needed to
One-rein stop fairly well
Rollbacks (we're working on it)
Barrels (fairly well)
WP (what I know of it, we're not good yet though.)
Back up (really well! It's his specialty! :P)
He has a soft mouth in his Oring snaff
He is pretty responsive to my cues
I can ride him bareback and bridleless (with only leg cues! )
Would you say he's ready to be moved out of a snaffle into a low port curb?