sexually active 的。 用官话就是:women who got the vaccine after becoming sexually active may not get the full benefit of the vaccine if they had already been exposed to HPV.
至于年龄,只要没有性经验的,都应该是有好处的;25岁一说,潜在的假设应该是到这个年龄还没有性经验的应该是在少数了;而且从25岁开始,女性就可以参加子宫颈涂片筛检了。以上是基于英国的情况。