Considering that Mendez speaks in clipped sentences, it seems likeliest that he meant Pike at timepoint X was the age Kirk is now.
That's how I always figured it, but it was a careless bit of writing that could have been clarified with a few more words. If Mendez had described Pike as "about your age when he took command of the Enterprise
," we wouldn't be having this discussion.
That is the way I always took that line too. It makes sense because of what happens in the episode and can see Pike was in his 30s 11 years ago.