There comes an age where the twinkle of innocence disappears. If you're lucky, I suppose, it's replaced with a fire of passion. More often, it is supplanted with a cloudy, dead stare.
Is there anything sadder than growing up?
Keep your nose to the grindstone. Make something of yourself. There will be time for fun later. Work hard. Stay late.
Me? I've gone with gray hair and a cloudy twinkle. I may measure success with a different instrument. My nose has never come close to any grindstone.