花开堪折直须折,莫待无花空折枝
Hua Kai Kan Zhe Zhi Xu Zhe, Mo Dai Wu Hua Kong Zhe Zhi
Ah Gu translation: When you see a flower is blooming, and you may pluck it, go ahead. Don't wait till you are left with the twigs.
爱惜时光,莫要错过青春年华。
Ah Gu Explanation: Treasure your time, don't put the most valuable time of your whole life to waste.