I adopted my male Rottie at 2 1/2 years old. When I got him he only knew sit and shake - and neither one was consistent.
He has since learned down, stay, come, leave it, watch me, stand, speak etc.
We went ahead and enrolled in a formal obedience class 4 months after I got him. So, it certainly is not too late! I recommend getting into a formal class though, you learn all kinds of neat things you might not think of on your own (such as if you give a command do not repeat it more than once and make sure you can make your dog follow through with it etc).
It's great fun to have a dog who is well behaved, especially such a big dog. Mine too pulled me around on the leash when I first got him, but training and a prong collar taught him that was unacceptable.
So start looking for a class to join!
