If i'm still growing at 18, what can i do to maximize my growth spurt?

Tanner stage: Your stage in puberty (tanner staging) determines when your growth plates will close, and once that occurs, growth will cease. Except in cases of growth hormone deficiency there's not much you can do to impact this. If you haven't reached a normal adult height yet, see an endorcrinologist.

Healthy lifestyle: You are most likely to reach your tallest potential height by following a healthy diet, getting appropriate sleep & and remaining physically active.Nothing specific you eat or drink will add inches .You can stunt your growth by the opposite, poor diet/sleep/inactivity can all take a toll.