Don't worry about being slow at first. We all had to start somewhere and you will definitely speed up. My advice would be to continue at your own pace, and don't try to work too quickly, as it will lead to mistakes or a shoddy job.
Don't believe for a minute you are not cut out for this game. The first one may have taken you 4 hours, but you stuck at it and you are improving your speed already, so that's a real positive step.
I have been in the game for over 18 years now, and can still only do 2 an hour (OCD has a little to so with this), and being in my 50s, am not about to get any quicker! If anyone tells me that I'm not cut out for this because I am too slow, let me tell you that I have built my second window cleaning business (from scratch) in one of the most economically deprived areas in Ireland in the middle of a recession, and have done ok.
If I can do it, there's no reason that anyone with enough drive and determination can't do the same or better.
Best wishes,
John