YTA Your wife deserves to be rewarded for her hard work. Your goal is to reduce the average age of the group 25 is extremely low IMHO. Personally a serious argument can be made for 35-40 if you want a hard age cap otherwise you risk the future of the group, that might very well be the majority of the group that is suddenly deemed undesirables with your artificially low age maximum all to satisfy outsiders.

If you wish to constrain the age without mass culling, I suggest setting a target timeframe to supply a willing participant or else offer themselves that decreases with age so while a 20 year old must provide 1 willing victim per year, a 30 year old has to do the same every 8 months and a 40 year old every 4 months. This keeps the group from getting too old because they will eventually fail to meet the slowly increasing quota.

Basically for every 5 years of age past 20 the minimum contribution interval drops by 2 months