Several release dates:
Luigi
1st Appearance: Mario Bros Arcade, 1983
1st Solo Game: Mario is Missing, July 1993
Notable Appearance: Super Mario Bros 2 USA, October 1988
Peach
1st Appearance: Super Mario Bros, October 1985
1st Solo Game: Super Princess Peach, 2005?
Notable Appearance: Super Mario Bros 2 USA, October 1988
Waluigi
1st Appearance: Mario Tennis, August 2000
1st Solo Game: ?????
Notable Appearance: None
As you can see, Luigi has a ten year gap between his debut and first solo games, while Peach has twenty years. However, this means we could be waiting until about 2020 until a Waluigi game, unless Nintendo manages to sneak him into a Wario game.
But then:
Diddy Kong
1st Appearance: Donkey Kong Country, November 1994
1st Solo Game: Diddy Kong Racing, 1999
Notable Appearance: Donkey Kong Country 2: Diddy Kong’s Quest, December 1995
However, Diddy Kong only had to wait 5 years for his shot in the spotlight (?), so a Waluigi game could be coming sooner than we thought.
Whoo... long post!
''If Timmy has seven apples and Peter has five apples, why don''t they just shut up and eat?''