Input im gonna give seems to be in the minority here. Having said that, i have had many MANY pullets of various breeds go broody & hatch chicks. Easter eggers, australorps, welsummers, marans, rhode island reds, buff orpingtons, production reds, red & gold sex-links (yes some have!), at 7-8 months. The youngest was a cuckoo marans that started laying at 24 weeks. I swear she laid 6 eggs then promptly went broody. She was an excellent first-time mother. She (Matilda) is now 5 years old & still raises chicks every year. I did always give the pullets bigger eggs from more mature hens. (Not small pullet eggs). Never once did i have a pullet quit setting, & ONly once did a pullet (production red) attack a chick as it was hatching. I didnt know i was "supposed" to let the pullets get older before hatching, & ignorance was bliss! I agree that after a broody has hatched her first clutch, she knows Exactly what she is doing, & there is no need to worry. But it seems like that would be true no matter the age of the broody? Personally, i would be more concerned about possible current cold winter weather than the age of your pullet. Yes the broody will keep the chicks warm, but u will need to keep drinking water warm-ish (so chicks dont get chilled.) You will also need to watch the chicks closely the first 48 hours to make sure they are strong enough to keep up with & go under the broody hen for warmth. Otherwise, chicks can quickly get cold, disoriented and die. And of course dont let mama hen or chicks get wet. Not discounting the expertise of others input, just saying all my dozens of broody pullets through the years have been excellent mothers. (With the exception of the one).