Another vote for change the instructor, its not on, or professional for someone in authority to be belittling at any stage of your flying training, let alone at the beginning. And you are their customer, they should want to keep you. You arent (it seems) in the RAF and being demanded by an employer to reach a certain standard in x hours.
I know someone in their 50's who completed their PPL in something like 200 hours. OK, thats way above the national averages, but he was enjoying the training, he wasnt particuarly quick to learn, and although his instructor was a pretty tough cookie, the instructor made personal allowances for his student, and got him successfully through the PPL. Both were happy, and you should be happy.