Excellent game design: The thing that gets you closer to your goal (getting taller so you can reach the golden apple) is also the thing that brings you into more peril (getting more vulnerable to the rocks!). Lots of games take advantage of this mechanic and it's great. Well done! Congratulations to me too because I reached the golden apple. A thought: As you get taller, it gets more and more difficult to react in time to red apples / rocks. It becomes impossible in fact - I'm sure the needed reaction time could be as low as 50 to 100 milliseconds - and it also requires a mouse movement, not merely a click. How could this be improved? Something to think about for a future version! 

It's a fun mechanic and it's well implemented.

I would suggest make the goal about half the screen, maybe a little above. Right now the goal is too high and the end game is basically moving around randomly, if a rock falls on your direction it's very difficult to react in time.