Teeth can be moved at any age as long as the teeth and gums are healthy. Adults are not usually eligible for NHS treatment so most commonly have to pay for treatment. This gives a wider range of types of braces that can be used.
The expectations from treatment may be different in adult patients, e.g. adults may want different treatment endpoints. This is something that should be discussed with you by your orthodontist when outlining the treatment options.
For more Information you can download the BOS guidance booklet.