Ken, no plumage characters (including "squareness" of tail) can be be used
in the field to tell the age of female Redstarts........ and hardly any in the hand at
this time of the year for that matter.
To my knowledge any perceived "greyness" or "brownness" is caused by light conditions/
, quality of photo (in this case impaired by strong direct sunlight) and
individual variation/degree of wear rather than being an age related factual change from "grey" to "brown"......
If you have evidence of the opposite, do by all means
enlighten me......(but please without distorting my True Colours
)
Peter