I think it's very realistic.
Last year I went from riding in Spring 6-7 miles maybe twice a week to a century in September followed by a very hilly and tough metric century in October. In June I did another century and am now training for two hilly metrics and another September century.

Just take it slowly, and work progressively on your training and comfort level on the bike. You have 6 weeks til September. If you handle this right, 50 mile ride will be a joy.