Carnival and Royal Caribbean cruises introduce new age ban and it spells bad news for young travellers

There are big changes in the world of cruise ships. In particular, it focuses on who can travel on the world's largest cruise lines, namely Royal Caribbean and Carnival Cruise ships.

Hands down the top two players in the multi-billion dollar industry, a ban of sorts has been introduced across the two cruise lines that regularly set sail from the Port of Miami in Florida.

The cruise ship capital of the world, it entertains ships from both companies on an almost weekly basis. And if they aren't in port, they're already out sailing around the likes of the Caribbean, Europe, or even the wider world if you're on the nine-month cruise of a lifetime.

For those ever thinking about a cruise, better make sure you check the rules now that they've been significantly changed for people heading out on to the open seas with either Royal Caribbean or Carnival.

A Carnival cruise ship in Sydney Harbour (James D. Morgan/Getty Images)

What is the new age ban and rule change?

Both Carnival and Royal Caribbean are cracking down on young people cruising with them.

It's bad news if you're under the age of 21 and leaving port in the USA.

But don't kick off too much. You're still okay if you're travelling with someone else under the age of 21. But things get tricky if one of you isn't of age.

No under 21s are allowed on their own (Daniel Perez Garcia-Santos/Getty Images)

What if one traveller is under the age of 21? And exceptions?

If someone under the age of 21 wants to travel with Carnival or Royal Caribbean, they must be accompanied by someone who is older than 25.

They have to be a relative or 'guardian' but they do not have to be the legal guardian of that person.

You're in luck if you're married and both under the age of 21, with those people exempt from needing a companion aged 26 or older. You'll just have to present your marriage certificate as evidence.

You can get around it if you're under 21 and married (Joe Raedle/Getty Images)

What have the cruise lines said?

Carnival says: "Guests are required to be 21 years of age [on embarkation day] to travel on their own. Guest ages will be verified at embarkation. Guests not conforming to this policy will result in denied boarding, and no compensation will be provided at embarkation.

"Guests 20 years of age and younger must travel with a relative or guardian 25 years of age or older."

Royal Caribbean's website says: "Royal Caribbean's minimum age to sail unaccompanied on sailings originating in North America is twenty-one."

For Royal Caribbean cruises departing from anywhere but the USA, the age is 18, so it is very much just an American rule.

If you've already booked and fall foul of the new rules, we would suggest contacting your travel agent or the cruise line directly for advice.