At age 37, I took about 30 hours to go solo. I am now at about 37 hours, and if I was to make the call myself, I would say I was ready to go solo at about 35 hours. I think the instructor sent me up 5 hours to early, but they did that for a very good reason.
I started flying late September 2013, and took 6 months to get to solo. So, 18.8 hours in 8 months does not sound bad to me, but I dont know your age or your backround.
Talk to your instructor. I was told to fly as often as a I could otherwise you spend to much time in revision. I am still low hours, but I can assure you this is so true. I have a 2 week break and its a huge setback.
Like johnjohncafe said, its about decision-making + situational awareness. When you can do both, they will send you up alone, even if your technique is not the best.