He's listed as 5'7.5 and 170lbs.
We can probably at least assume he'll be between 5'8 and 5'10 when he's done growing. His height doesn't matter as much as his weight, considering he's a forward unlike his dad. As long as he's around 200lbs when he's full grown than he could be a very decent mid to late round pick.
Count on Boston to take a chance on the little man. Remember, St. Louis wasn't even drafted!