We are in a college town and we have a pretty flexible age requirement. Since we are in a college town and most 'prospective' students of the 3 colleges are typically under age 18 (some as young as 16) we do allow teenagers to come, because their parents will become future repeat guests. And we do not turn them away because they always come with a parent who is coming along to see the schools. We have never recieved calls from teenagers wanting to rent a room, its mostly the parents who are calling for them. And we have had quite a few people who are newly weds stay here that are 18-20 years of age. None have ever been a problem.
We typically do not allow any kids younger than 5 years of age unless:
1. The whole house is rented by the family. For like a family reunion, graduation, etc... That way if it is a younger person, like a baby who cries and fusses all night, all the people staying are family/friends and so they are a bit more understanding about infants. They are also less likely to complain, because their family.
2. If a family who has a baby calls and they are not coming with other family members and no other guest rooms rented, then we would allow it. But if even just one room is rented by a different guest (especially a University client) we tell them no.
Thankfully there are enough hotels in town that peole with kids can go and stay at.