Is swinging legal?

Yes. In Europe swinging is legal between partners over the age of 16, though most swingers, swingers clubs and swingers parties enforce a rule that you must be over 18 to join their sites and parties. In the USA, the age varies between 18 and 21 depending on local laws.

In most other democratic countries swinging is also legal. The main exceptions being Islamic states which forbid swinging at all. It is still possible to find swingers in Islamic countries where people risk everything to exercise their natural human rights to have contact with other people without interference from religious extremists or politicians.