Goodness, 5 months is practically still a baby, lots of growing to do yet! I would probably not let them brood that young, either! I'd also be concerned about how committed they would be to the whole process. One of mine that I let brood young (I think she was around 9 months old?) was not great with the entire process and caused me a whole lot of stress while she was incubating and rearing her babies! Constantly letting the eggs roll out behind her in the nest, wanting to abandon her newly hatched babies for eggs, going to bed without leading her babies in with her so they were lost and cold, etc.

Then again, the full adult hen out of the same line that I let brood this year was also terrible at mothering, so hard to say if that was age or genetics in my case, I suppose.