Factually-speaking, "too young to breed" can only mean one thing: she hasn't matured enough to come into her first heat yet.
The rest is just opinion and personal preference.
Jack
PS: I have bred
many outstanding bulldogs (Champions, producers of Champions, etc.) using first-heat bitches.
Gr CH Zukill came out of Zsa Zsa's first heat at 11 months. I believe
Waccamaw's Ch Big John came out of Sabre's first heat as well.
Eli Jr./
Bullyson came out of a 10-month old Spook.
Ch Mr. Serious ROM came out of LuLu's first heat.
Gr Ch Awesome Beast ROM came out of a first-heat gyp bred by a woman who never rolled a dog before.
Conclusion: Breeding young bitches can produce every bit as good, or better, dogs as breeding "hard-checked" or even Champion-level bitches ... IF you have a truly well-bred bitch ... and IF you know enough about the dogs in the genetic background to breed them correctly. If you don't, then you shouldn't breed any gyp at all until you know enough about what's behind your gyp. (PS: Best practice, though, is to evaluate your bitches before you breed them, just to see if they have the traits you desire. You can only take shortcuts for so long before they'll catch up to you!)