Mazer’s a senior citizen, but he’s basically a kid at heart – by which we mean that he enjoys beating up Ender.
Actually, maybe we could say that Mazer shows a possible end for Ender. Throughout the novel, until he shows up in Chapter 14, Mazer isn’t so much a man – he’s a legend. Yeah, he’s the guy who beat back the buggers’ Second Invasion. And that’s pretty much the end that Ender moves towards, becoming a legend for beating back the buggers during a third invasion. (Check out in Chapter 15 when the colonists are practically worshipping Ender.)
Mazer’s also the guy who didn’t act according to the rules: he was court-martialed twice. (Being court-martialed once may be unfortunate, but being court-martialed twice looks like carelessness.) Which kind of sounds like Ender, who also doesn’t totally listen to the rules. (Although let’s be honest, they both follow a lot of rules. They’re pretty good at a lot of things, but they’re not the best at being rebels.)
What else is interesting about Mazer? Well, like Ender, he gets to know the buggers really well from fighting them. Also like Ender, he lives longer than he normally would, thanks to relativistic travel (should be said with an echo, so it sounds big and important). That is, because he travels near the speed of light, Mazer lives only eight years when the rest of the world lives fifty…so, basically, he traveled into the future and left behind all the people he knew. (The comparison to Ender would be Ender and his brother Peter. At the end, Peter is an old man while Ender is barely beyond his teen years.)
So Mazer is a pretty good model for Ender in some ways. But there are at least two things that seem to set him apart. First, he manipulates Ender into fighting a real war by telling him that he’s actually practicing on computer programs. Ender, in comparison, simply isn't that manipulative. (Or is he? Maybe Mazer treats Ender the same way Ender treats Bean and his other soldiers?)
Second, just like Graff, Mazer expresses some real affection for Ender and a belief in Ender’s goodness (14.308, 14.399). Whereas Ender – well, do you think Ender kind of hates himself? Mazer is sure of Ender’s innocence (just like Graff), but Ender’s not so sure.