That's not accurate. There is a years post draft and age restriction for college students. It isn't like I could go and take summer courses and finish my degree at age 20 and be a UFA.
Also, if a team wants to sign you and you're a 20yr old non college player you are better signing with that team than re-entering the draft. All elc's are the same and there isn't a guarantee you get drafted again. The NHL draft is notorious for undervaluing overagers.