are these reatty to pick and eat yet.

are these reatty to pick and eat yet?
also If I only cut off half of it will it grow back?

If that's leaf lettuce, yes. You can pick them at any time. You can also just peel off leaves individually and use them (they sure look ragged after a month of harvest like that though).

Cutting the main rosette and leaving a very small chunk in the middle will generally result in regrowth if you have cooler conditions in my experience. Doesn't always though.