No, its perfectly fine to reach goals or ones you've had for most of your life, but its absolutely crucial that you make new goals to work towards. Its the same if you give up or change your mind about a goal, it has to be replaced.
From what I've heard (not my expertise) the brain chemistry primarily rewards the pursuit, not as much the outcome. I've been there a few times myself after both achieving and deciding to drop a major goal (because I learned more about the outcome that made it no longer desireable). Having no major goals is an almost certain recipie for clinical depression among other issues if one is not found quickly to replace it. I believe its because the intrusive thoughts of fundamental questions like "what is my life's purpose" now definitely have no answer in your own head.