'Mae' has NOTHING to do with English, it is technically a two-syllable word (both a and e are strong vowels in Spanish), and it used to be 'maje' which was then shorted to ma'e, which was the most common spelling even a decade ago.
Yes, it comes from the verb 'majar', and many Ticos (Costa Ricans) especially of older generations consider it improper to use this word in polite society.
The national debate over this word even finds its way into the editorial pages of the national newspaper La Nación.
As others have said, the word is constantly heard among the youth along with huevón and a few others. A feminine form, rarely heard, is majita.
It is a little rude to call a female 'mae' but it happens. It's just like calling a girl 'dude' in English. Either way, 'mae' is here to stay.
Finally, although a fair number of Ticos around San José and in tourist areas speak passable English, they are very proud of their Spanish heritage and language and apart from a few specific words like 'email' they don't speak much Spanglish at all there, but try to sound educated in whichever language they are speaking, which is almost always Spanish unless talking to a Gringo or practicing for English class.