What is the universally accepted standard of flexibility that you should compare yourself against?

There is not such thing as a universally accepted standard of flexibility because there's no material that is taken as a reference point. You can't say it's twice the flexibilty of rubber or twice the flexibilty of bamboo or anything similar because no official reference points have been established in the SI system.

There is no absolute measure of flexibility.

10/10 recommend bring pads/tampons with you no matter what. im 16 & i’ve had mine since i was 12 and they’re still it regular, but id suggest using the glow app, many women use it for fertility reasons but i use mine specifically for the period tracking portion and it guesses when your next period will most likely be for the next two months. i dont believe theres any way to delay your period, so id say hope for the best but make sure to bring all of your stuff just incase. have a good cruise!