奋斗吧，少年 can be translated to English as "keep striving, young man". It's a quote from a famous Chinese essay written by journalist Lu Xun in the early 20th century. The essay is called "My Old Home" and it's about a young man who is struggling to find his way in life. Here's an English translation of the quote:

"Keep striving, young man. Don't be discouraged by the difficulties you face. Remember, every great achievement is the result of persistent effort."

Here are a few example sentences using this phrase:

"Keep striving, young man. You can achieve anything you set your mind to."

"Don't give up, no matter how hard things get. Keep striving, young man."

"Life is full of challenges, but if you keep striving, young man, you will eventually reach your goals."