Danes have a very liberal attitude towards sex. This is reflected in the laws and in personal behaviour. The legal age for consensual sex between adults is 15.
Do not, however, mistake openmindedness for a lack of moral standards of disregard for decency. Treat everyone with respect, accept a no for a no and play safe.
Visitors with HIV are welcome to Denmark, but if you infect your partner through unprotected sex you may be prosecuted and sentenced to prison. Public sex is frowned upon and you may be arrested, so be discreet if you feel the call in the wild. Topless bathing is acceptable for women and nudity is permitted at most beaches. Have fun, just mind your manners and take care of yourself and the people you are with.