Of my 5 girls:
Mikayla had her first at 11 months, 2nd at 16 months, 3rd at 22 months, still waiting for her next (so far she's at 8 months since her last and nothing yet)
Brooklyn had her first at 14 months, 2nd at 20 months, 3rd now at 2 years and 6 months...so she didn't have her first until 14 months, she had her 2nd 6 months later, and now 9 months later she's having her third...lol
Hadley had her first at 10 months, 2nd at 16 months, 3rd at 22 months, 4th at 2 years and 4 months (she's the ONLY regular girl so far)
Maddie had her first at 9 months, she's due in January...so we'll see...
Sophie is almost 8 months, and nothing yet...but she'll be spayed soon so I doubt she'll have one at all...