me and my friend are plannin a trip to cancun and when we go i'll be 20 and she'll only be 19... would we still be able to book a room and check in since we're over 18 or do we have to be at least 21 and older?
For the most part you will be fine. Some resorts do require one person to be over 21, but this is mostly during spring break. From now till early December is the lowest part of the year, so I doubt you will have problems. Now if you want to be sure you won't have any problems, once you know which resort you want to stay at, contact the resort directly
