I was born in 2000, so the President by that time is Bill Clinton (the 42nd President of the United States from 1993 until 2001).
I know these voice actors and the writers of the show what year do they were born on, and I know who's the President by that time there:
Tara Strong (Twilight Sparkle) - 1973; Richard Nixon (37)
Ashleigh Ball (Applejack, Rainbow Dash, Blythe Baxter (LPS)) - 1983; Ronald Reagan (40)
Andrea Libman (Pinkie Pie, Fluttershy) - 1984; Ronald Reagan (40)
Tabitha St. Germain (Rarity, Princess Luna) - 1976; Gerald Ford (38)
Cathy Weseluck (Spike, Mayor Mare) - 1970; Richard Nixon (37)
Nicole Oliver (Princess Celestia, Cheerilee) - 1970; Richard Nixon (37)
Shannon Chan-Kent (Pinkie Pie's singing voice, Silver Spoon) - 1988; Ronald Reagan (40)
Rebecca Shoichet (Twilight Sparkle's singing voice, Sunset Shimmer) - 1975; Gerald Ford (38)
Kathleen Barr (Trixie) - 1967; Lyndon B. Johnson (36)
Kazumi Evans (Rarity's singing voice) - George H. W. Bush (41)
Peter New (Big McIntosh) - 1971; Richard Nixon (37)
Michelle Creber (Apple Bloom, Sweetie Belle's singing voice (season 1-3)) - 1999; Bill Clinton (42)
Madeleine Peters (Scootaloo) - 1996; Bill Clinton (42)
Claire Corlett (Sweetie Belle) - 1999; Bill Clinton (42)
Chantal Strand (Diamond Tiara) - 1987; Ronald Reagan (40)
John de Lancie (Discord) - 1948; Harry S. Truman (33)
Kelly Sheridan (Barbie, Starlight Glimmer) - 1977; Jimmy Carter (39)
Britt McKillip (singer, Princess Cadence) - 1991; George H. W. Bush (41)
Carly McKillip (singer) - 1989; George H. W. Bush
Andrew Francis (Shining Armor) - 1985; Ronald Reagan (40)
Lena Hall (singer, Countess Coloratura) - 1980; Jimmy Carter (39)
Kristin Chenoweth (Princess Skystar (upcoming movie character)) - 1968; Lyndon B. Johnson (36)
Emily Blunt (Tempest Shadow (upcoming movie character)) - 1983; Ronald Reagan (40)
Michael Pena (? (upcoming movie character)) - 1976; Gerald Ford (38)
Uzo Aduba (Queen Novo (upcoming movie character)) - 1981; Ronald Reagan (40)
Liev Schreiber (? (upcoming movie character)) - 1967; Lyndon B. Johnson (36)
Zoe Saldana (Captain Celaeno (upcoming movie character)) - 1978; Jimmy Carter (39)
Sia Furler (singer, Songbird Serenade (upcoming movie character)) - 1975; Gerald Ford (38)
Lauren Faust (writer, animator) - 1974; Richard Nixon (37)
Daniel Ingram (composer) - 1975; Gerald Ford (38)
This topic right here is the question that who is the President of the United States by that time you were born. And to make sure that the year you were born on is the right vote on the poll above between the years of the presidential term.
UPDATE 2/11/2017: Rename/rephrase topic, no need to have the date on this topic what date they're born on, additional characters, and sentence rephrases.
UPDATE 7/27/2024: Added poll choice "44. Barack Obama (2009-2017)".