While they may be 18, I would not call them kids. At 18, they are old enough to join the Army, Navy, Air Force, and Coast Guard and put their life on the line. If we consider them old enough to make that kind of decision then who are we to judge whether a 20 year old is old enough to fly for an airline? Age is just a number. I've know 18 year olds who were more mature than 40 year olds and I've flown with 800 hour pilots that were better than 8000 hour pilots.