Yellow squash gets harder as it grows, and it grows very fast. About 8" long by 3" to 4" in diameter is about the maximum size for it to be tender enough to eat; we usually pick it before it gets that large. You will learn quickly by looking and feeling the squash if it is nearing that point when it will be too hard to slice or eat.

The crookedneck squash with bumps tends to be a little harder than the straight-neck, but that shouldn't matter.

Don't be afraid to pick it at different sizes/stages just to see what works best for you. As long as you keep your squash plants watered, they will grow more squashes to eat. Just be a little careful to not damage the plants when you harvest. The leaf stems are somewhat fragile.

Gourmet-style is to pick it at about 3 to 4", even bumpy squash are quite tender when that young. As a rule of thumb, use your fingernail to press gently a half-inch below the stem. If you can make an indent, it's tender enough to use skin and all, otherwise plan to peel and remove the seeds to roast separately.

Yes, pick it tiny! The bumpy yellow crookneck gets so seedy even when under 8 inches. I wouldn't touch it unless 5 inches or less. At that size, they are tender and nutty in flavor.