Just like with people, some dogs have earlier growth spurts, some just grow at a slower but steadier pace, and some have spurts for longer periods... it's actually much healthier for a puppy NOT to grow fast, as this puts a strain on their musculoskeletal systems, and can cause pain, inflammation, and things like arthritis in adult life. And they continue to fill out and gain muscle mass until as late as 2 1/2 - 3 years, so until he's 18 - 24 months, you won't have a definite idea of his adult self. But even if he doesn't reach 26", he's very close... you should post some photos, so people can see what he looks like!