birthday on a cruise ship

Age is just a number -- except when it comes to milestone birthdays. Then, it's an excuse to celebrate in style. A cruise is the perfect way to welcome a big birthday, whether you're looking to let loose, kick back and be pampered, or check something off your bucket list. (Kayaking around glaciers in Alaska, anyone?) We've rounded up the best cruises to take when you hit 21, 30, 40, 50 and beyond. Have your cake and eat it, too, with our top picks for milestone birthdays.

You're turning 21: Carnival, Royal Caribbean, Norwegian

Celebrating your 21st birthday at some superficial pub is so overrated. Your first (legal) drink should be on a cruise. Grab some friends, and plan a few days at sea on one of the big three: Carnival, Royal Caribbean or Norwegian Cruise Line. These lines are not only some of the most wallet-friendly, but they also offer plenty of opportunities for poolside bumming, recreational fun and late-night entertainment -- including some of the best cruise ship nightclubs. Just remember to celebrate responsibly.

You're turning 30: Celebrity Cruises, MSC Cruises

While your wild days might be weaning, that doesn't mean you can't put 'adulting' on hold for a week and "treat yo'self." Celebrity Cruises and MSC Cruises (particularly its newest ship, Meraviglia) offer classier onboard atmospheres and higher quality dining, without sacrificing fun. When the mood to let loose strikes, head to the ship's disco. While MSC tends to have a livelier nightlife scene, Celebrity Cruises heats up at least one night per week (on most ships) with silent disco parties, in which everyone dances to music via headphones set to different DJ-run stations, as opposed to loudspeakers.

You're turning 40: Oceania Cruises, Azamara, Viking Ocean Cruises

You work hard. You deserve to feel spoiled on your 40th birthday. Luckily, you don't have to break the bank for a little special treatment. A few cruise lines -- including Oceania, Azamara and Viking Ocean Cruises -- offer upscale experiences at moderate prices, compared to ultra-luxury lines. Although they're not entirely inclusive (you'll still have to pay for certain perks such as select specialty restaurants and alcoholic beverages), you can still enjoy a taste of the high life, with sumptuous dining options, elevated service and a more immersive experience on land.

Whale watching

You're turning 50: Expedition Cruise

At 50, you've still got plenty of time to accomplish all the wild escapades and dream vacations on your bucket list -- but why wait, when you can 'go big' now? An expedition cruise is the perfect way to celebrate this milestone birthday, as it offers a combination of relaxation and adventure, with a handful of "bucket list" experiences you won't find on a big ship. Un-Cruise Adventures and National Geographic's Lindblad Expeditions are both good places to start, as they offer a broad scope of itineraries, including Alaska, Costa Rica and the Galapagos Islands.

You're turning 60: Europe River Cruise

They say 60 is the new middle age, so what better way to embrace your youthful spirit than with a port-intensive river cruise? European itineraries are by far the most popular, and their sightseeing opportunities -- cosmopolitan cities, castles and vineyards -- make them a great option for first-time river cruisers. (Here's how to choose which one is best for you.) In terms of cruise lines, you can't go wrong with Viking; although it doesn't offer much in the way of onboard activities. More active travelers should look to lines such as AmaWaterways and Avalon Waterways (among the affordable options), and Tauck, Uniword, Scenic and Crystal for a more luxurious experience.

Dining on a Silversea cruise

You're turning 70: Regent Seven Seas, Crystal, Seabourn, Silversea, SeaDream Yacht Club, Windstar Cruises

Imagine not having to bear specialty restaurant fees or tally how many drinks you've purchased. For your 70th birthday, you deserve the utmost in luxury -- a cruise that includes all your meals, drinks and activities, with no questions asked. You can find this on lines such as Regent, Crystal, Seabourn and Silversea, and the more intimate SeaDream Yacht Club. Windstar Cruises, another small-ship luxury line, is a great choice for those who don't want to go overboard on their spending; the only caveat is drinks are not part of the package.

You're turning 80: World Cruise

Spending more than 100 days at sea might sound like a dream, but we think it's the perfect way to celebrate this milestone birthday. World cruises have gained quite a bit of popularity in recent years, and more lines than ever offer the chance to hop from continent to continent, visiting exotic ports along the way. You'll pay a pretty penny for the full cruise, or you can save some cash by booking a segment, offered by some lines. Either way, the experiences and memories will be priceless.