To keep things simple, I have a historical series (in which the history is near identical to ours with a few differences) with fantasy elements. The fantasy elements stem from the main characters being immortal*, and each immortal has their own 'gift' or 'miracle' they can perform. I focus on the third generation of the immortals who were born between the 1400s to late 1600s. My question is should I start this series, starting somewhere in the 1500s where the characters are slowly introduced, developed, meet other immortals from previous generations, and go through different time periods? Or, should should I start in the 1900s, where they are mostly developed, and the central conflict to the series really starts to pick up?