After a bird reaches maturity, it is very hard to estimate age with any certainty.
Some signs can indicate wear and tear that older birds often have (or very poor living conditions for a younger bird).
If her leg scales are flat and tight, she is likely younger. If her overall look is bright eyed, smooth wattle/comb, full feathered, glossier, plump, she is likely younger. Younger hens will have slightly smaller combs that are rosy pink rather than true red if they have not come into lay (although anemia from worms or poor conditions will also cause pale combs and different breeds have different size combs).
You can gauge her readiness for laying by the width between her two pelvic bones....3 to 4 finger width indicates a laying hen. Two or less, non-laying hen. If she isn't molting, and has only 2 finger width, with smaller, rosy comb, and overall looks healthy, she is likely a younger pullet.
A laying hen's vent has a stretched "smiley" appearance while a non-layer's vent looks small and puckered. Older spent hens (especially in rescue situations) generally look haggard, rough, craggy and spent.
Sexually mature girls will do the egg squat while young pullets will not. Old hags often will no longer squat.
But again, once a hen reaches sexual maturity, it is very hard to tell their age. Many of the non-productive signs above can be poor husbandry and ill health rather than true age. Even an older hen well cared for can be productive, albeit not as prolific as her younger years.
I'll ink a good video article below on determining if a hen is ready to lay or productive.
She is a pretty girl. Good luck with her.
LofMc
