When is my spinach ready to eat? I have never grown spinach before.

Hello bekind
Spinach leaves can be harvested any time from your plant. Just clip the largest leaves, leaving the rest of the plant to grow. The more mature the leaves, the more flavor.
Yum ! Here come our salad days.

And better be hurry. Seems like yours start bolting. Sometime it get bitter when bolting.

I would pull the ones that are starting to flower