If you want comfort, stability, control, better balance, and safety, it’s advisable that you choose a mountain bike that suits your size. This will depend on your height.
Mountain bikes are always measured in frame size which is given in inches. Sizes range from small (13”-15”), small-medium (15”-17”), medium (17”-19”), large (19”-21”), and extra-large varying from 21” to 23”.
[ On a side note, if you aren’t sure which size to choose, read this mountain bike size guide]
These bikes make it easier for you to handle them in rough terrains due to their small frame.
Keep in mind that whenever you are buying, and when on top of it, your legs are able to touch the ground. This is to ensure better balance when riding.