[Red5]

The use of uppercase for the first person singular is aa manuscript convention that appears in Middle English to differentiate the first person singular from an ordinary lowercase letter; otherwise the first person singular often appears to be part of the preceding word. It's pretty easy to be confused this way, especially since word spacing isn't always optimal in manuscripts, and in very early mss., there is no word spacing.

I can't give you an exact date for capital "I" becoming formal practice. I can tell you that "I" isn't capitalized in the Cotten manuscript of Layamon's Brut, which is roughly 1208, (where I is still often "ich") but it is capitalized by the late fourteenth century Auchinleck manuscript. These are the two extremes that I have readily at hand.

From: http://nielsenhayden.com/makinglight...es/002611.html