Depends how old you look.....
I just turned 23 and I've been playing in Atlantic City for awhile now and I've NEVER been carded.
If you look old enough and you're not causing a ruckus and you're betting low limits you'll probably be ok. However, if you're winning and they think you're counting or cheating, I'm sure if they thought carding you would get you to leave they'd do it.......