In general, most of the employers who advertise on CoolWorks require that employees be at least 18 years of age. This is especially the case for companies that provide on-site housing and require staff to live on property (as is the case with a lot of the National Park employers due to their remote locations far away from rental housing availability).
However, there are always exceptions. Jobs that are occasionally posted on the Teen Jobs page by employers that are able to accept applications from candidates under the age of 18. (If this page returns an error, it is because there are not currently any eligible jobs being advertised there).
Also, if you find an employer that does not require staff to live on site or does not provide housing (e.g. an company in a ski town or area where you already live and don't need housing), you may be able to apply. Carefully review the job requirements to see if there is a minimum age (this is common for jobs where handling/serving alcohol or operating vehicles/machinery is required). If you don't see an minimum age requirement listed, just reach out to the hiring contact to quickly ask them if you'd be eligible.