Mettam has no fixed address, and is currently a prisoner at HMP Lincoln.
He appeared today at the Lincoln Magistrates Court, and the case was sent to the Lincoln Crown Court for August 13. Mettam remains in police custody.
The incident occurred on July 1, at around 7pm, on Viking Way, which is at the back of Bentley Drive, leading off Vauxhall Road, in Bracebridge Heath.
The woman was walking along the road when she was approached by a man who sexually assaulted her. Police called the incident serious, and called for witnesses to come forward ever since.
An e-fit of the man was also released a few days later (medallion), on July 5. Police also increased their patrols in the area in the evening.