Citizen Archivist: transcribe US National Archives documents and tag photos
A US National Archives programme for volunteers: you can transcribe historical documents, tag archival photographs and share comments with other members of the National Archives Catalog community to make the materials easier to find. Participation requires registration following the instructions on the programme page, after which you can pick tasks among the Citizen Archivist Missions. The page states no limits on age, country or timing.
Volunteering Free Online