fig, ax = plt.subplots()
ax.plot(var.index.to_datetime(), var.total, 'b', label='Variance')
ax.set_ylabel('Variance of log wages')
ax2 = ax.twinx()
ax2.plot(shares.index.to_datetime(), shares.average, 'g', label='Average Age')
ax2.set_ylabel('Average age')
lines = ax.get_lines() + ax2.get_lines()
ax.legend(lines, [line.get_label() for line in lines], loc='upper center')
ax.set_title('Wage Variance and Mean Age')
plt.show()
Legend only shows one label when plotting with pandas