@Kaivosmies - You can perform Uni-variate Analysis with the Sales variable alone, like describing patterns in the data which include Central tendency (Mean, Median, Mode) and Dispersion of data (Range, Variance, Standard Deviation etc.). You can also create Histogram & Box-plot charts to see the graphical summary of data distribution.
Next thing you can do is to perform a Bi-variate analysis, which will include both Customer Age (Independent) and Sales (Dependent) variables. You can calculate Correlation Coefficient or you can fit a Regression Equation between these two variables. For graphical representation you can plot both of these variables to a Scatter Plot and see the relationship.
Hope this helps.