First of all, if they are 7 months old, they must have been hatched November/December, which is a very odd time of year for turkeys to hatch, unless you are in the southern hemisphere of course? As I usually hatch in May/June, our turkeys are over 7 months when they come into lay in March the following year in response to lengthening days. As the days are now shortening in the northern hemisphere, I am not sure what effect that may have.
So, you probably need to let us know where you are, what you are feeding, and how much day length the birds are getting. If they are in a dark shed with no natural daylight, that will affect them. I am pretty sure that turkeys should be capable of laying at 7 month given the right conditions.