Marvel logic. Gotta love it.?

Wade Wilson at the age of 18 (?+) goes on mission with Wolverine (because at the age of 18 you're a f**king elite soldier right? because you can get into army at like.. 10 years old yeah O_o). Ok, YEARS pass, he gets cancer, offers for experiment, gets all scarry and turns into Deadpool. Again, by Marvel logic, he is 18 years old. (his body may be regenerating constantly so he doesn't age, but what that doesn't make him 18 years old. and f**k me if that's the body of an 18 year old). More time passes, blah blah, he is still 18. Because Marvel's infos say so. I'm missing the logic here. Sorry if I seem arrogant/ignorant but from all I've read it just doesn't make sense. Also could I have an approximate real age please? If possible.