Young people - pluck the blossom when it is ready; don't let opportunity slip by.
Tips
history
From 《金缕衣》 (attributed to 杜秋娘, Tang dynasty): 劝君莫惜金缕衣, 劝君惜取少年时. 花开堪折直须折, 莫待无花空折枝. Chinese carpe diem - don't cling to wealth, cling to the prime of youth.
usage
堪 = 'can be / fit to be.' 直须 = 'simply must / at once.' Both are classical constructions still used in literary Chinese.