I'm 25, is it still worthwhile to get the HPV shot?

Absolutely! The hpv vaccine protects against a virus that is responsible not only for genital warts, but for almost all of cervical, penile, and anal cancers, as well as 70% of mouth and throat cancers. It's better to get the vaccine now rather than never!
Yes! Yes, as long as you remain sexually active and are getting exposed to the hpv virus. The shot is officially approved between the ages of 9 and 26. The likelihood of infection by age 50 is 80% for all women, so I would see your doctor and start the vaccine series.
Yes. The hpv vaccine has been shown to be effective at your age. It won't prevent hpv from arising if you have already contracted it (and 85% of us have hpv-most just don't know it). I would highly recommend the vaccine to prevent any future infections.