My lad started by sitting on a little potty when he first started - around two and a half. But he wanted to copy his daddy, so soon learned to stand up. Used a stool so he could be high enough. Probably started doing that a couple of months in to training and has never looked back (so around age 2.5). He never really had problems with aim, even back then, he was so proud to be like daddy he wanted to do it right. He's now 4 and can reach no problems without a stool and is now very good at it having done it so long.
One thing about teaching them to stand up BEFORE they master their no.2's, is that you then find it hard to get them to sit at all in order to do a no. 2. So if you haven't managed to train that yet I would encourage still sitting down so that you can master that first before they get to stand up.