Hi. I must say that this is indeed one of the amusing questions I have come across in recent times. Growth of facial hair is under hormonal control - male hormone dependant and further increases with age in some till they are in their late twenties. Also largely depends on genetic and racial factors.
If you are having decreased growth due to any disease, it can be taken care of. Otherwise all you have to do is just have a good balanced diet, good fitness workout at least thrice a week and take care of your beard as it grows in length with shampooing, gentle combing and even conditioning of necessary.
If you need any further assistance in this regard let me know. Take care.