as such there is no restrictions of age.hotels here can provide you 2 weeks visa which can be further extended to two more weeks.Sometimes , for some nationalities , thre is difficuilty in getting visa,so u can try to any five star or four star hotel which they agree to give u visa and accomodaation.some names of five star hotels are intercontinental,movien pick,shelton,regency etc,further u can find by giving command in googles hotels in doha,try to get cheapest rate by calling more than one hotel especially four star or three star hotels