“Variants: Any man who is under 30, and is not a liberal, has no heart; and any man who is over 30, and is not a conservative, has no brains. Show me a young conservative and I'll show you someone with no heart. Show me an old liberal and I'll show you someone with no brains. If you are not a socialist by the time you are 25, you have no heart. If you are still a socialist by the time you are 35, you have no head.”

Source: Wikiquote