I must admit I thought cruises were for the "older" person so was a little apprehensive about being in the minority. I needn't have worried as the age range was incredible, it really is a holiday for anyone from 0 to 100 years old.
The whole experience from being picked up at the airport at the start of our holiday to being dropped back at the airport at the end was superb. We were extremely well looked after by all staff at all times. The currency onboard is £s but all payment is made to your boarding card. There is a 2% surcharge for using a credit card so it's best to settle up with a debit card or cash.
Once at sea (in international waters) the onboard shops are allowed to trade. They are fairly expensive as you'd imagine, but if you buy on the "offers" night it doesn't work out too bad.