Names cycle on roughly a hundred-year curve. The names that felt elderly in 1990, Hazel, Florence, Theodore, August, now feel fresh, because the generation they actually belonged to is mostly gone, and the association resets.
Girls' vintage picks rising fast
Hazel, Florence, Pearl, Ada, Edith, Beatrice, Cora, Mabel, Iris, Eleanor, Clementine, Genevieve.
Boys' vintage picks rising fast
Theodore, August, Arthur, Otto, Felix, Hugo, Walter, Frederick, Wilfred, Atlas, Casper, Silas.
Still too soon
Names from roughly the 1950s-1980s, Linda, Susan, Gary, Brian, are still too close. They'll come back eventually; not yet.
Picking one without it feeling costume-y
Pair vintage first names with modern or neutral middle names. "Florence Wren" lands; "Florence Eugenia" tilts twee. Modern surnames help too, vintage + vintage + vintage stacks up.