Tony James pleaded guilty to aggravated sexual assault, three counts of sexual intercourse with a young person and one count of indecent assault.

Handing down the sentence in the Supreme Court in Hobart yesterday, Justice Shan Tennant said James formed the relationship via text message with the East Coast girl between March and June last year.

He introduced himself as a 20-year-old builder named Andrew Free, and when the two exchanged photos, he sent an image of an attractive young male.

Justice Tennant said James later told the girl he was 38 years old, and then travelled to visit her in the June school holidays and met her parents.

''You told the complainant that you had cancer and that treatment had aged your appearance,'' she said.

Justice Tennant said the man flattered the girl, telling her she was beautiful, and made her ''infatuated and dependant''.

''She depended on the contact you maintained with her, describing feeling sick and sad if there was a break in that contact,'' she said.

''You manipulated this young girl from the start.''

The girl ended the relationship after the pair had sex in a Bicheno hotel room and she filed a complaint with police.

James was interviewed by police last August. In November he spent the night with the girl's 17-year-old friend.

Justice Tennant said she was not convinced the man would avoid relationships that involve either emotional or sexual intimacy with girls.

James was jailed for 12 months and will be eligible for parole in July. His name will be placed on the sex offender registry for five years from his release.