As an NM myself, I find that a bit of a stretch (to put it mildly).
I feel that I am in the same ballpark with FMs (indeed, I did fairly well against them on my old account). But IMs are definitely a big step above me, and GMs are another leap above that (not that I ever got the chance to play more than a handful of those...but even so, the point was made clear enough).
I know I'm often the labelled a bad guy for pointing these kinds of things out, but the USCF archives show you as unrated with a membership that expired last year. In fact, the highest-rated Clifton in the database was a "Joseph Clifton" at 1801 from way back in the 1980's.
Well, I wouldn't call you a bad guy so much as more than a trifle naive (for thinking that that's really my name...not to mention for not getting the joke that it implies). It's okay though, you're far from the first one around here to make that mistake. And you've managed to be a good deal more civil about it than many in the past have been.
I have come across one or two players who made a sudden advance at age 50+.
Not to world class tho'.
No one beats their best shoot-em-up score after reaching 14. And mathmeticians who have not published anything world shattering by about 22 know they never will.
If you want a satisfying game at which you can continue to improve up to 80+ bridge is for you. :)