Personally I believe yes. Wait until you’re old enough to legally drink and old enough to have adult problems you both have to face together on a regular basis. A lot changes in your early 20s, if it’s meant to last forever then you’ll last forever no matter what, better to wait and be sure than rush into anything.
Personally i'm not married so i cannot speak from experience, but i think that the fact you're thinking about marriage is actually appropriate as you said and i quote " I am 20 and dating the love of my life for 3 years this month." Now you clearly love your significant other and want to be with them, but always remember marriage is a completely different world than dating, personally i would take a bit longer to consider it and if you feel comfortable with it maybe discuss your expectations and desires to your significant other sharing is always number one in a relationship next to trust and honesty. but ultimately you asked is it to early to get married my opinion is no but only if you both are truly ready dont rush into something just because it seems like a good idea.
i really hope this helps,
i hope you two have a long and happy relationship