Healthy if short

Wondering if this plant is doing well at almost 4 weeks , little short?

Strain? Looks like a healthy Indica I wouldn't worry about it.

Looks healthy. It’s an Indica, isn’t it?
How many nodes/sets of leaves?
If you’re taking it all the way through indoor it seems a little smaller than some for it’s age, but I only get mine going indoor, then transfer to greenhouse/outside, so a slow start/weaker lighting doesn’t matter as much as they end up in the sun.
An indoor expert here will help you, if that’s your route.

It's a purple haze strain, working on its 4th node . Total indoor grow

You can slowly vegetate it, or you can blast it with lights and nutes to grow fast. The important thing is that it is healthy and trained/shaped/trimmed up when you switch it to flip the light schedule to flower.
Assuming it is photoperiod and not autoflower.

Looks perfectly healthy. Some plants just grow quicker than others. Doesn't seem to be any indicator of quality though. I've had plants that are smaller than that at 4 weeks and turned out to be killers, and my current indica hybrid is massive at 22 days, and might turn out to stretch by the looks of it. Some plants will shoot up very quick third, fourth or fifth week.

The pics attached Is a 21 day fat monkey auto. Have heavily tied it down as it seems to be stretching, but would be around 12/14", and onto 4th node. It was tiny 8 days ago in the smaller pic, but over 8 days it has gone insane.

You'll probably find it will take off very soon.