Estimates of up to 70% of people have hpv.There are more than 200 strains of hpv, yet, gardisal only helps prevent about 4 strains. How is that it is even called a hpv vaccine?
Well, it's only a few strains but it's the major ones. The estimate is more than 70% of HPV cases but it's expected to be higher.

As I said it's no magic trick. If you have HPV it won't work, if you avoid HPV then your very lucky, if you have another strain it may not work. You might be 20 and die of cervical cancer or just get your cervix cut up, your much more likely to get it if your 80 but noone deserves to die of cancer no matter their age. There are much much nicer ways to pass.

Still the vaccine has the potential to save a LOT of lives.