Yes, you are too old to sell this.
What you need:
10 ripe lemons
1 cup sugar
1 cup water (for syrup)
more water (to dilute)
Slice lemons in half. Squeeze into a small bowl until you have made a cup of lemon juice. Set extra lemons aside.
Combine sugar and water in a saucepan over medium heat to create a simple syrup. While the two are heating, pour lemon juice into the bottom of a pitcher. When the syrup is ready, add that, and dilute to taste with water.
Slice the remaining lemons into disks. Add these to the pitcher, too. Refrigerate at least 40 minutes.
Not fancy enough? Try one of these combos: