EXCLUSIVE

Courtney Stodden turned 18 years old today ... which means she can vote ... or play the lotto ... or accept any one of the FOUR offers she's already received to be a HARDCORE PORN STAR.

Stodden -- who married a 50-year-old actor when she was 16 -- has been shamelessly teasing her lady parts for years ... exploiting the hell out of her underage sexuality in the hopes of staying famous.

Now that she's "legal" -- at least 4 porno companies are hoping she puts her money (and a whole lot more) where her mouth is ... offering her lucrative XXX contracts.

One of the companies is Brazzers.com ... which says it wants to "showcase [her] talents" by featuring her in a scene with male porn star Keiran Lee ... who Brazzers describes as the man with the "million dollar penis."

Stodden also got an offer from Babes.com ... which says it already penned a porno movie specifically for Courtney based on her real life experience. The flick is called, "Happily Humping My Hubby."

TMZ obtained a copy of the script, which contains the following line for Courtney:

"I may be young but I can s*** a d*** like a much, MUCH more experienced s***. I’ll d*** t**** it, l*** his b****, do whatever I gotta do to get that m**** l*** all on my f***."