No future Astros, only former Astros with birthdays today ~
RHP Tom Griffin (65)
A first round pick by Houston in 1966, Griffin pitched for Houston from 1970 to 1976, going 45-60 in 199 appearances (123 starts) with a 4.20 ERA and a 1.470 WHIP. In his rookie season in 1969, he led the National League in SO/9 at 9.6 in 31 starts. Griffin's best season for Houston (arguably) was in 1974 when he was 14-10 in 34 starts. Ironically, he was also fifth in the National League in wild pitches that year. In 1980 and again in 1981, he led the National League in hit batters while pitching for the Giants.
SS/CF Eric "Cool Breeze" Yelding (48)
Yelding played for Houston from 1989 to 1992, batting .249 over that stretch. In 1990, he stole 64 bases (behind only Vince Coleman and Rickey Henderson), but also led the MLB in caught stealing. In 1992, he was sent to the White Sox for LHP Rich Scheid. Yelding was a first round draft pick for the Blue Jays in 1984.
3B/2B Russ Johnson (40)
Yet another first round draft pick with a birthday today, Johnson was drafted by Houston in 1994 and played for the Astros from 1997 to 2000 before being traded to Tampa Bay for RHP Marc Valdes. His best season for Houston was 1999 when he hit .282/.358/.442 and was 1-for-1 with a walk and a double in the NLDS.
LHP John Halama (41)
Halama wasn't a first round pick like all the other birthday boys, but rather was drafted in the 23rd round by Houston in 1994. He started 6 games for the Astros in 1998 and went to Seattle at the end of the 1998 season as the player to be named in the Randy Johnson trade. According to Baseball-Reference, on July 7, 2001, Halama pitched the first nine-inning perfect game in Pacific Coast League history for the Tacoma Rainiers, a performance which led to his being recalled to the majors.