Lombardozzi turns 23 in a month. 3.5 years difference. Don't forget, Antonelli made the majors in 2008, flamed, had a tough 2009, then missed 2010 due to injury. The Nats bought low, which is why he is on a minor league contract. Put another way, Antonelli made the majors roughly in the same time frame as Lombo would if he were called up in September.
Me, I kind of like a guy who is still on the up side of his peak years getting the shot first when his numbers are better and the younger guy has shown a big drop in plate discipline. Both could be major leaguers, but Lombo looks like the bigger failure risk this year / next year.