Synonyms for the word 'seasoned', broken down into two categories: good and bad.
GOOD:
accomplished
adept
battle-scarred (scars are cool and chicks dig them, right?)
competent
expert
familiar
knowledgeable
matured (pretty sure not the same as old)
practiced
prepared
pro/professional
qualified
skillful
tested
tried
wise (beyond your young years!)
worldly/worldly wise
BAD:
been around (only for it's physical implication)
hardened
old hand (because of aforementioned distaste of 'old')
toughened
trained (just makes you sound like a poodle or seal)
vet and/or veteran (again, 'old')
weathered (like a house in Maine? no thanks)
Hope this helps Matt