Hey Billy,
At just 20 years old, you have plenty of time for your beard to continue to develop. As to beard growing genes, it is very possible for men within the same family to have various beard patterns and differing growths. I did some research earlier on both beard inheritance and characteristics which I will re-post below:

Inheritance: One of the biggest questions asked is: Where does a man inherit his beard traits from – his mother or his father? Many people believe that beard genes are carried on the x chromosome coming from the mother’s side. It is not that simple. While there are sex linked genes governing such things as colour blindness, haemophilia and baldness, beard genes do not fall into this category. I did a google book search and was able to find some beard genetics info in snippets from the following books: Basic Genetics: A Human Approach by Joseph McInerney and Genetics by G. Archunan. I then cross referenced the terms and concepts they were talking about to get more info on the web. Here’s what I found. Beard genes are not carried on the x chromosome and are present in both sexes. Beard development is actually considered a sex-limited gene, as it is a trait activated by the hormones that are present in a male. A woman given the same hormones could grow a beard based on her own genetic pattern as well. In regards to inheritance, McInerney specifically points out that beard development genes are passed on to a son from both the mother and father (page 103).
Terminal Length: Hair Growth and Disorders by Ulrike Blume-Peytavi states that terminal beard and moustache length is typically 50-300 mm (approximate 2-12 inches) while terminal scalp length is typically 100-1000 mm (approximately 4-40 inches) (page 10). All hairs go through cycles of growing (anagen – growing phase, catagen – transition phase and telogen – resting/shedding phase). http://en.wikipedia.org/wiki/Anagen#Hair_growth_cycle_times. The greatest factor affecting terminal length is how long the anagen (growing phase) lasts which is genetically determined. That is why some men can grow beards much longer than the typical estimations above. I also believe it is very possible that terminal length may increase with age, but I have not found specific evidence of this yet.
Seasonal Changes: Blume-Peytavi cites a study of 14 Caucasian men with significantly higher beard growth rates in summer as opposed to winter months; he suggests that natural fluctuations of testosterone (more testosterone = more beard growth) cause this (page 28).
Development: Rodney Dawber in Diseases of the Hair and Scalp states that beard & body hair development go on over decades as vellus hairs become terminal. (page 9). More specifically he states that, “Beard growth is maximal during the fourth decade and remains much the same thereafter.” (page 9)

If you get a chance, you should definitely grow your beard out. That's the only way you can truly see your own potential.
Welcome and good luck,
- Fred

You either live life -- bruises, skinned knees and all -- or you turn your back on it and begin dying - Christopher Pike paraphrasing Dr. Philip Boyce (Star Trek - "The Cage")

Bearded in BC's Thread