Is it ok for an 18 year old girl to marry a 46 year old man and is it legal and possible and they both have a lot in common and are great friends?

In most US states, this would technically be legal.

Everywhere in the universe, however, it would almost certainly be a spectacularly bad idea. If a girl at 18 has "a lot in common" with a 46 year old, it's a good bet that she won't when she's 28 and he's 56. (Any 46 year old with "a lot in common" with an 18 year old is probably grossly immature... she'll likely grow out of being immature, but he's pretty much already missed that particular train.)