what do you think is the minimum laying age for my hens?

not likely especially in the summer heat. I would expect any eggs tip at least 24 weeks.

 

I had 3 17 week olds and one has already been laying. The other two keep checking out nests boxes but are panting like it's HOT...which it is!

 

My Buff O surprised me at 16 weeks.

 

give them at least 6 months.... Last time I raised RIR's it was almost 8 before they layed their first egg, course it was 101 degree Texas heat then....