I use to work in the hotel business for over 5 years and have worked in some way with pretty much every hotel in Omaha, with the exception of Motel 6's and Super 8's. The age to book a hotel room in Omaha proper ranges from 18 yrs old to 21 yrs old. Of course it depends on what hotel you wish to book, but most hotels that are considered 3 star and up will book a hotel to a person the age of 19 yrs old.
You just have to do your homework. Some hotels still hold strict to the "must be 21 yrs old to book rule." Again, have to do your homework before traveling and taking the chance.
Now, if you're using hotels.com or travelocity.com the following rule applies:
"For most hotels, the primary guest must be at least 18 years of age on the day of check-in. If the minimum age requirement is older (usually 21 or 25), it will be listed in the Hotel Description, under "Amenities" or "Know before you go."
Its always best to read the fine print before committing to a purchase from said sites. That way it saves you time, money and you don't have cancel on clients. Plus, it saves the clients from wasting time and using up a great excuse.