It's hard to tell without cutting into it.
Early season okra is usually pretty tender as long as it get proper water. The later the season gets, the tougher the okra.... No matter how much water. I tend to pick it real small in the later parts of the season. I keep the pickles for myself in case they are tough. The smaller they are, the more tender they'll be.
If my knife meets any resistance when I cut, that okra pod is trashed. I've been so busy and tired the past few weeks that what little okra I'm getting is worthless... Time to plant some beans!
USDA Zone 7b/ Sunset Zone 31