Poland issued a stamp on 5th September 2015 to commemorate the Optimist World championship 2015 held from 25 August to 5 September 2015.The Optimist is a small, single-handed sailing dinghy intended for use by children up to the age of 15. The Optimist is recognized as an International Class by the International Sailing Federation. Optimists are used for beginners, but most sailors continue to race them up to 13 or 14 years of age. The age limit is 15. Very small children are sometimes “doubled up” but usually the boats are single-handers.