I think you're fine, it depends on a lot of things. Your instructor might be proceeding through the syllabus with a different emphasis, or perhaps he/she may feel the instances in which he/she would have been ready to send you to the blue skies solo, the weather or other elements were a little more aggressive than he/she would have liked. I remember feeling restless the day I thought I would have a chance to do my solo touch and go's and the cross-winds were aggressive for a pre-solo student pilot so my instructor did not give me the go, which was appropriate.
Your instructor will be the final judge on this, but provided a mild weather day, your instructor's convinction on your satisfactory completion and mastery of the fundamentals for solo phase, I submit you're ready to solo and it will inmensely boost your confidence and motivation towards the completion of the rest of your training. Good luck, and don't worry about the hours, like I said, weather, instructor approach to the syllabus and personal factors affect the total time before solo, nominally at 20 hours you're more than fine. If you were at 30 hours you would be running behind the power curve or the instructor is not appropriately challenging your progress. So you're doing good. Keep up the work, good luck man.
