The HMS Victory, it started being built in 1759 and was launched in 1765
being 256 years old, it is the oldest sailing ship still in commission
Armament

Trafalgar:

Gundeck: 30 × 2.75-ton

long pattern Blomefield 32 pounders

Middle gundeck: 28 × 2.5-ton long 24 pounders

Upper gundeck: 30 x 1.7-ton short 12 pounders

Quarterdeck: 12 x 1.7 ton short 12-pounder

Forecastle: 2 × medium

12-pounder (5 kg), 2 x 68-pounder