If you're happy then do what you want, but in my personal situation as a near 30 year old man there is no way in hell I would ever marry a 20 year old.
The life experience gap is just way too much. A 20 year old girl is still barely out of high school, has never been with actual men to compare you too, she was maybe with a few teenage boys? Meanwhile as a 30 year old man i've been with numerous grown women and at this point in life when I see that right one it's easier to tell if that is the right one. A 20 year old girl on the other hand 4 or 5 years down the road is gonna have that doubt set in, it's human nature. This person has never even sat down at a bar and had a drink, never experienced really jack shit when it comes to life, but she's supposed to commit to you and only you for the rest of her life? lol that's just setting yourself up for failure.
In my personal situation I could fill up a book with stories of all the life adventures and experiences i've had, a 20 year old girl can tell you about high school lol
Give me someone who has actually ventured out and lived life so when they see me they can compare me to all the other actual men they been with and can say "yep InfamousICON is the one for me, he's better than all the others".
But like I said at the beginning if you're happy then do you, but at the end of the day you might end up with years of your life gone and a massive alimony payment every month (cause you know damn well a 20 year old more then likely isn't bringing much to the table at the beginning).
Have fun with that homie and good luck, hopefully you're one of the few where this works out, but statistically you might be fucked.