How old were DJ, Stephanie, and Michelle in the first season of "Full House"?

Donna Jo "D.J." Meredith Tanner (b. 1977) is Danny's eldest daughter. She is 10 years old when the series begins and 18 at the show's end.

Stephanie Judith Tanner (b. January 1982) is the middle daughter. She is 5 years old when the series begins and 13 when it ends.

Michelle Elizabeth Tanner (b. November 1986) is the youngest character on the show, and is played by twins Mary-Kate and Ashley Olsen, who alternate unnoticeably in the role. Michelle is Danny's youngest daughter, the "little princess" whom he tends to spoil and pamper more than the other girls. She was just 9 months old when the show began and 8 when the series wrapped.

https://en.wikipedia.org/wiki/List_of_Full_House_characters#Stephanie_Judith_Tanner