Your term policy should cover you till the age you plan to retire.
Here's something you should keep in mind that will help you understand this better:
Term insurance is like a replacement of your income when you are no more.
So you need to stay covered only till you have financial responsibilities and your loved ones are dependent on your income. That's all. You don't need to pay an extra premium amount by staying covered longer than that.
So, if you are a salaried individual, your age of retirement would typically be 60-65 years (unless of course, you plan to retire earlier). Your plan should cover you till then.
If you are an entrepreneur, your retirement is more likely to be much later. So, you may want to cover yourself for a longer duration till the time your family is dependent on your income.
And if you are a homemaker, you should stay covered till your children or your ageing parents or anyone else who is dependent on you financially or for your caregiving will become independent.