Yes, gas has mass and takes up space, so air is matter. Any substance that has mass and takes up space is called matter. A desk is matter. Oxygen in the air is matter. The floor is matter.
Milk is matter.
Things that you can see, touch, or feel are different forms of matter. The amount of space an object takes up is the volume of the object. An ant is tiny. The ant takes up just a little bit of space. It has a small volume.