Hi and a belated welcome to this great forum & website,
Unlike many on this forum including MPG Im a relative newbie to FH research having only been involved a few years, but from my readings I've always understood "full age" to mean 21 years or above, and that applies back to 1800 or so.
Thankfully it seems others share this view, this first link makes good reading as it distinguishes between "full age" and the altogether different legal marriage age and so on. Indeed I've seen an example of a bride claiming to be of "full age" when actually only 16, so..??

http://www.rootschat.com/forum/index.php?topic=199256.0
http://www.ancestryaid.co.uk/boards/genealogy-coffee-room/18372-full-age-18-21-a.html

Hope this helps, good luck with your continued researches, Jeff

under age , full age and consent

http://www.forum.forest-of-dean.net/index.php?id=23597