I rarely comment but I couldn't resist after seeing some of the comments.
Firstly, ignore anyone who says it'll be full of over 60s, they have clearly never gone on a cruise or the wrong one.
Of course, some cruise lines are aimed at older people but most aren't. Like Oceania or Holland and America.
I'm early 40s and my wife is mid 30s. She had never done a cruise before we got together so I booked one as she was open to trying it. She was close to tears leaving, she didnt want to get off. I booked a back to back for her 30th on a cruise and it's one of her favourite holidays.
Do you know the cruise line and ship as that's a big factor?
For example, Royal Caribbean are full of 20s to 50s and its aimed massively at families. We have done a few in the past. We did the Symphony in October around the med and loved it. We actually stayed on the ship at some ports as the food was free, loungers easy to get and my pick of any jacuzzi.
Celebrity are my favourite, the food and entertainment are amazing. I doubt you'll get better in a hotel. We've done loads of 5 star hotels but cruise dining is way above. You'll have about 10 restaurants, some are free and some have a small fee. Like, we may do a steak house or tappanyaki and pay £25 each extra, but that's rare as the foods that good.
Norwegian are also great, my second favourite. P&O are OK, not to the level of RCL, Celebrity or Norwegian.
Find out the cruise line/ship. If its Beyond, Symphony, Allure, Oasis, Escape then I've done those and they are amazing.
My wife and I love to travel. We now do a cruise, then a travel one where we backpack. Like, last year we did Japan and then a cruise later in the year.
I've done loads of beach holidays and on 46 countries and I'll be honest, a cruise is always top of our list. I'm not saying this to brag, just for context. I can give an opinion based on experience, not what I think it'll be like.
My best friend always does beach holidays. He likes getting a villa in Greece or Spain and I got him on a 4 day cruise last August. He wasn't keen. Wasn't looking forward to it, thought it would be full of posh people. He's booked his wife and kids on a Royal Caribbean cruise this August. He loved it.
So, find out the ship and watch some videos.
The entertainment on some is amazing. One night we watched an ice skating show, then watched Hairspray and at 11pm watched the diving show which was just ridiculously good. You'd pay money for all those if you weren't on a ship.
Enjoy.