I was fortunate enough to attend on of Zach Allen's games earlier this year and shake hands/offer my congratulations on a well played game afterwards (I'm the author of that TNIAAM post that was linked here in September). I am 6'0" tall and would say Zach is in the 6'2" to 6'3" range. I'd also say that 185 seems about right. He's pretty skinny, but has a very strong, wiry, athletic build.
In addition to noting that Zach's Temple team plays in 5A, the highest level in Texas, they also went out of their way to schedule hard out of conference games. They beat Austin Westlake (the game I was at), a perinnial power (alma mater of Drew Brees and, more recently, Nick Foles of the Eagles) and Southlake Carroll, the preseason #1 team in all of Texas. A quick googling shows that Southlake has 4 starters on defense that have accepted scholarship offers from FBS schools. Suffice it to say, Allen has gone up against strong high school competition. I love the fact that he'll get to Syracuse in January. I'm hopelessly biased, but in my mind the only question is whether Zach redshirts a year before taking the reigns or if he'll jump right in.