Bo Dallas, The son of "IRS" Mike Rotunda was born on May 22, 1990 it makes him the first ever professional wrestler born in the 90s to enter a Rumble match.
His father's first Rumble appearance was in the legendary 1992 Royal Rumble for the WWF title won by Ric Flair in Albany, NY. At that time Bo was not even 2 years old yet.
Note: An earlier version of this post listed Dallas as the youngest ever Rumble competitor. That was an error and we apologize for any confusion.