my husband is mid 50's, i'm late 40's. we have sailed Celebrity twice, once to Alaska - Galaxy, and once to the Caribbean - Horizon. These were 7 and 11 day cruises, respectively. Last year went on a New England/Canada cruise w/RCCL, 10 day cruise. So far we prefer Celebrity although the RCCL Grandeaur of the Seas was a very nice ship and would sail with them again. We really enjoy the sea days so this should be a great, relaxing cruise.
To answer your question about boarding...i would imagine that we would be able to board in the afternoon. to be honest, i didn't realize that it left that late, not that that makes any difference. We live in Virigina and have never been to San Diego before so will take some time to do some sightseeing before sailing.