there is no race to go solo, and your FI will judge when you are ready and SAFE. remember you are flying on his/her licence.
many students are ready at about 15 hours, some take 50 or more. once you leave the ground on your own you have no choice but to land it yourself, and nobody is going to let you go solo without a very good chance you and the a/c will come down safely.
remember to get your medical done, and most clubs want you to have passed air law as well.