I remember back when the vaccine was still in clinical trials and I was watching the HPV vaccine news with baited breath that the reason Merck made the cut-off at 26 was their preliminary studies (nowhere near clinical-trial-sized n) showed the efficacy started dropping off significantly right around there. Sadly I can't find the links I read back then, so it's entirely possible I got bad info. What I can find is that Merck's clinical data is for women age 16-26 and boys and girls age 9-15, meaning they either don't have any data for women and men older than that or they don't have data that supports their product for women and men older than that; I can't tell you which is the case. (A an aside, the science geeks might enjoy actual data in PDF format).

Incidentally, GSK is making a big deal out of the adjuvant used in Cervarix, AS04, which is considered more effective than the one used in Gardasil (better immune response, much less likely to need a booster shot in the future). There is also a Cervarix vs. Gardasil study being conducted by GSK, so confident they are in their beloved adjuvant.