Wife loves cruises I am a take it or leave it guy.
I'll disagree on sea sickness a cruise has no motion..Ive never seen anyone get sea sick on a cruise, except the one time we went almost through a hurricane.
25 years isnt old for a cruise ship as they are majorly renovated every 5-10 years and repowered (drive engines and generators) usually every 7.
Honestly for a first time cruise age of ship shouldnt even be in your top 20 questions.
but...if you are driving to charleston, it is just another 2 hours to Jacksonville and one of the biggest cruise ports in the US. Miami, Lauderdale and Canaveral are better cruise ports, imho because you get longer at first port...but you wont notice the difference on a first cruise.
Actually for someone who has never been to the bahamas a cruise is a great way to see a little bit of 3-4 islands and see where you want to return and spend more time.
Dont do the "first cruise" Nassau, free port and key west so many do out of Charleston. It sucks. Nassau has its bad ass but not near the port. Freeport is Durham on an island without the nice areas of Durham.
Just know this, cruises arent all inclusive as far as drinks go. IF you are a big drinker, buy the $50/day all you can drink package and dont look back. I once ran up a 700 alcohol bill in 7 days...