First off, just because you have been trading stocks for 4 years, it doesn't mean you are good at it. However, your dad shouldn't have trusted you in the first place, but...
Why in hell would you recommend a 40ish+ man to invest 20k into a pump and dump penny stock? Even as stupid of an investment as it is, those types of investments should be left for the young ones who can handle the risk. Your dad obviously could not handle the risk and could be why he argued with you about the decision in the first place. At his age, most of his money should be in mutual funds and bonds. Sure, he can have a lot of stock too, but not penny stocks. What were you thinking? Even if it did go from 1 cent to 10 cents, good luck trying to sell it. And if it goes from 1 cent to 1/2 cent, good luck finding someone to buy it. His stock investments should be in secure companies such as apple and such. Stocks that pay dividends are usually a good rule to follow. However, many tech stocks don't pay dividends because they like to reinvest the funds, which provide for future growth.
You obviously did not manage your dad's funds correctly as you did not determine his risk level before you even invested the money.
But whatever... I've only been a finance major for 3 years and have only invested in a few stocks over the past couple years. But you have 4 years under your belt, so I guess I should trust you more...