Crooknecks and other summer squash are usually eaten at the immature stage, before they are ripe. You can eat them at a range of sizes, anytime before they get tough or the seeds are hard.

The smaller squash are more tender. Usually they will be really good between 6-8 inches long. Congratulations on your harvest!

The one on the left might be too old. Like Brittany said, it won't hurt you if it's old but it might be tough and not tasty. If it is old *enough*, though, it might be good for seed-saving. If the shell is hard.

The one on the right is good. You might be able to leave it on the vine one more day to get a bit bigger (they grow a lot in a day!).

My aim is to get them when they are as big as can be without being old, because I like to maximise food production :). But it's true they may be more tender when smaller. That partly depends on weather and stuff, too.

Those will probably be fine. About mid way between the two would be ideal.

Jim

Have you ever seen (or bought) crooked necks in the stores?

The skinn should nice and shiny(No bumps) and size about same as those sold in the stores.

Looking at your picture, I can tell the the one on the left has matured beyond a SUMMER squash. Squash on this kind should be harvested young and TENDER, like cucumbers.
The when you slice them, the seeds inside are SOFT.

Once their skin gets bumpy and tough, the seeds inside get too tough to enjoy. At the size of the one on the left in the picture, I cut them in half, scoop out the seeds with a spoon, grate them and add some grated potatoes and onions, an egg, a little flour, salt and pepper and make patties to fry. Excellent eating but a little more work than the young and tender ones.

Sandy

"Have you ever seen (or bought) crooked necks in the stores?"
No. I have never seen yellow crooknecks in the store, only smooth ones with straight necks. At a farmer's market occasionally but not in stores. Yellow crookneck is one of my favorite vegetables and is superior tasting to other yellow squash, IMO.

I like to pick crooknecks soon after they start getting bumpy. Then slice and saute in butter.

Jim