Nathan Sparling, 28, wants to scrap the existing legal limit on adoptions which means it is not an option for those aged over 18.
He said: “Adoption is not just about protecting the rights of a young child, but bringing together families in the eyes of the law. “
Mr Sparling, who wants to be adopted by his stepfather Brian, has submitted a petition to Holyrood as part of his campaign.
Adult adoption is currently legal in countries such as Canada, the US, Japan, Germany and Spain.
Mr Sparling said the Scottish Government could use its forthcoming Family Law Bill to make the change, and added he will urge MSPs on the Public Petitions Committee to back that call.
He said: “Having been brought up by my mum until the age of 12, my stepfather came into my life and raised me as his own.
“Unfortunately, due to the law that limits adoption to those under 18, when it came to looking into this as an option I was unable to take it forward.”
After raising the issue in the press, Mr Sparling said a number of people in the same situation had got in touch with him.
He said: “The convention of human rights enshrines the right to family life in Scots Law, however many feel that this right is not realised if you want to be adopted beyond the age of 18.
“Family life and the sense of belonging to a family are important features in our everyday lives, and therefore the law has to change to allow for people over the age of 18 to be adopted by their step-parents or foster parents.”