"Firstborns tend to grow up fast and they feel the pressure of the adults around them. When the parents are gone, does the pressure vanish? No. The firstborn continues putting pressure on himself. Firstborns are serious, conscientious, have strong powers of concentration, are list-makers, critical, perfectionistic, goal-oriented achievers. They believe in authority,may be legalistic, are loyal and self-reliant. Don't expect them to come up with many surprises.
This doesn't mean that every firstborn turns out identically. There are no clones. Actually there are two basic types: strong-willed and aggressive or compliant and wanting to please. The first can develop traits that make them the high achievers and hard drivers with lofty expectations and a need to be at the top. Compliant persons strive to please others and usually are very reliable workers. They feast at the table of approval."
(Understanding the Man in Your Life, H. Norman Wright, Word Books, 1987, pg. 34)