Same word as veteran:

adept, battle-scarred, been around, disciplined, exercised, expert, from way back, hardened, inured, knows one's stuff, long-serving, long-time, not born yesterday, of the old school, old, old-time, practical, practiced, pro, proficient, skilled, sophisticated, steady, trained, up to speed, versed, vet, weathered, wise, wise to ways, worldly