Pic, I know not yet but soon? Some is 18" tall

You can eat any onion "green", as you say you are just trading off freshness for size. Pull a few early and try it see if you think it is worth it. Cut the stem.like a scallion and try it if it isn't too hard yet. Try the fresher leaves cut up.

If you like it and think it is worth it, plan next year to plant enough to pull half early. If you don't think it is worth pulling some early, now you know. It's your preference.

Garlic does most of it's bulking in the last 2 to 3 weeks so you're losing a lot. If you're doing hard neck you can eat the scapes and they taste like garlic.

If you only have a small number of plants (as shown in the photo) it is probably not worth the gain-vs-loss to harvest the plants young. They would basically be garlic-flavored scallions... and if you might want such early Spring "garlic", I would recommend Chinese chives. Those have the advantage of being perennial, spread to form large clumps, and can be harvested from late Spring onward. Walking onions are also perennial, and are both the first & last veggies I harvest each year.

BTW, I just took a look at last year's walking onion bulbils. They are large, healthy, and beginning to sprout. If you might be interested in these "forever onions", just send me a PM.

I have about 20-25 garlic plants, so lots:) Those were the biggest. I think the only way to tell where they are at is to dig one up. So hard to tell how close they are to harvest until they are really close.