Welcome aboard, Laetitia! It sounds like your family is looking forward to setting sail to the Western Caribbean with Disney Cruise Line this year! What fun you have in store!
I'm sorry to tell you that the age restrictions listed with each
Port Adventure are very strict. You will not be able to book a child on an adventure unless he or she is the correct age. I understand that can be frustrating at times, as there have been some exciting adventures that I know my daredevil, and very tall for his age, 5-year old would absolutely love and do well on, especially because he could easily pass for a 7-year old, however the limits are in place for a reason and they are not able to be changed. In fact, the reservation system won't even allow you to add him to that Port Adventure reservation, as his age will not allow the computer to do that.
I suggest that when you continue browsing the different Port Adventures, you click on Family Adventures to narrow your selections down to the more age appropriate adventures available. You can even then click the Ages 5-7 box on the left of the Port Adventures screen to narrow it even more, however you'll need to double check the exact age limit of each particular adventure.
There are lots of others out there that I'm sure he'd love, Laetitia! And this might be a great excuse to re-book another sailing for a few years from now! In fact, if you re-book while onboard this cruise, you'll get a discount, pay a reduced deposit, and promotional offer of future onboard credit. Keep it in mind!
Good luck as you continue planning, and please stop back if you have other questions before you set sail!