Stats is a page where you can keep track of your game progress. It can be displayed by clicking the blue tab on the bottom of the game screen, fourth from the left.
From the Stats page you can find your Avatar (with gender switching option and customizable accessories like hair and hats), total time blocks, total money earned, total girls met (or activated), jobs unlocked, number of dates taken, number of hobbies unlocked, lover requirements, and number of hearts earned.
The Stats also allow you to reset the game. By resetting the game from here, your game will start from the beginning, losing your skills, hobbies, jobs, money, affection, and all girls except Cassie. However, you will still be able to keep your diamonds, achievements, time blocks, and store purchases. The benefit of resetting is the addition of a speed boost, allowing you to chat with girls, go on dates, and give gifts more quickly. It also allows you to increase skill levels more quickly in your hobbies and increase the speed of your jobs, which can earn you more money. The speed boost you would receive for a reset now is shown above the Prestige button, and stacks (meaning if you reset for 1x speed boost, and reset again for 1x speed boost, you would then have 2x speed boost).
You can reset at any time during the game.