The Toronto Maple Leafs have the fourth overall pick in this year's NHL draft. Mitch Marner is a consensus top-five pick. You do the math: Marner could, very well, become a Leaf.
He's also listed as 5'11", the shortest of the top-five guys - and the only one under 6'0".
While that shouldn't matter too much, size is definitely a concern when playing hockey; after all, it's a high speed, very physical contact sport.
The good news? We're talking about an 18-year-old boy; the chances of him being done growing already are pretty slim. If Marner's available, you don't hesitate to take him. After all, size is important, but talent much more so, and he definitely has the talent.