User blog comment:B214/Question & Answers 5/@comment-14.201.211.143-20160502132107/@comment-3435913-20160502143659

First, Gasper isn't hundreds of years old; Vampire societies are isolated from the rest of the world so their attire appears outdated which is probably where you made that assumption.

Rias presumably got her evil pieces at 13 (age of concent in Japan, but not age of adulthood which is 20). Reading through the storyline, Rias reincarnated her pieces in this order as of Volume 21:
 * 1) Akeno ("Scarlet and Crimson") - c. 6 years prior
 * 2) Koneko - c. 4-6 years prior
 * 3) Kiba ("May the Shine be on You") - c. 4 years prior
 * 4) Gasper - c. 1-4 years prior
 * 5) Issei - nearly a year ago
 * 6) Asia - nearly a year ago
 * 7) Xenovia - c. 9 months ago
 * 8) Rossweisse - about 1/2 year ago