''Yesterday is the past, tomorrow a mystery. Today is just a gift, hence it's called the present.''
Bottom line is, you never know when your time is up. So you should take the little time that you have and cherish it. Live like today is your last, 'cause tomorrow just isn't promised.. but yet you should try to keep the day after tomorrow in mind.
It's all about balance. If you have certain dreams and aspirations, you should try to keep reality in mind. Persue your dreams, but expect the worst.
Get married, have kids, and besides all that you can still try to achieve your goals. Because if you shut out the one, the other will be all you have leaving you with nothing to fall back on.
It's healthy to have dreams/goals/aspirations, however, you can't dismiss reality. Best thing to do, is to try to create a realistic world where you have the chance to persue your dreams.