I'm not an expert by any means, but I would think mid-twenties for a woman was considered old maid territory. Certainly not underage or young.
ETA: There's some interesting info here
http://www.faqs.org/childhood/Ke-Me/...n-and-the.html apparently after the Civil War the age at which people could marrry was raised from 12 for girls

to 16 and from 14 to 18 for boys. So 26 would be well into adulthood.