I've only been actively studying astrology for about a year, though I have studied occult, magical, and mystical things for at least 10 years. This background provides me a perspective on how astrology should be approached which directly impacts what really "makes" an astrologer. As I've mentioned several times here and there, I write my own astrological software. From the very beginning, I did not trust what someone else's programs might tell me. So, I decided to make myself proficient at the measuring and comparison of the positions of celestial bodies/points, which is really astronomy. So, in my mind, astronomy is the first half of astrology and the interpretation is the second half.
After about a year, I would say that I am more proficient than average at understanding the movements of things seen in the heavens, though I am certainly not the best at interpreting them. Because I base my software on the Swiss Ephemeris (which is a modification of calculating software originally written by NASA's JPL for the long-term tracking of complex planetary movements), I can give solid positions and directions (even velocities) for exact times. It provides a lot more information than is normally used by astrological software (for example, I can determine which way the Sun is "leaning" around the gravitational centre of the solar system), though most astrological software packages are pretty close to accurate for what they provide.
In short, I've never felt that I've achieved higher than an intermediate level of competence at any of these things I've studied. It seems to me that those who are convinced they know are the ones at the greatest disadvantage. The ability to continue learning is what makes a student a good student. The minute that hubris slows you down, you stop being a good student.