Plant to small for age?

Totally fine! Autoflower will surprise you. They seem to grow no faster than a normal photo. Here in another week or two, they'll grow nonstop till they finish. Expect some signs of her sex in the same time period. Once she starts showing sex, she'll get growing fast. Like noticeable growth every week. I'd make sure that she starts getting whatever will be your maximum light exposure by next week. Full sunlight from now on.

They look pretty reasonable for their age, having said that I'm no expert on Autos. Just be careful about putting too much stress on them as you're essentially on a timer when it comes to the plant going into flower. There is no substitute for natural sunlight so they should love that, just be careful about nasty critters munching on them outside. I would do some research on IMP (integrated pest management) for the outdoors, this video is a good place to start www.youtube.com/watch I would check out the whole video series if you want to get into organics. Jeremy is super pro and a really good teacher.

Looks healthy. Around 4 weeks is when I’ve seen them start to take off. Every plant is different. Make sure they are getting good light and not overwatering.