I'm leaning towards 49, for similar reasons to horselydown86.
Other examples of '6' have evidence of the pen stroke starting upwards, followed by an anti-clockwise curl into the main down stroke - a kind of hook or loop. In some cases this is very faint, but I can't see it at all in this one.
The point or angle at bottom left also seems very similar to the one in '4'. By adjusting things like levels, brightness, contrast and gamma I can't get it to disappear, but it stays remarkably similar to the one on the line above. (Contrast Thomas Nunn, 3 lines above.)
(Sorry, the image is a bit wide, but I think it's needed for clarity. Scroll right to see the ages.)