Yes, it is normal for men's libido to decline to varying degrees as they age. However, most men in their 60s and even 70s should still have some level of sexual interest.
Aside from age, decreased libido can sometimes be caused by other factors. For instance, depression and significant stress often lead to a lower sex drive. Endocrine disorders that cause hormonal imbalances can also result in reduced sexual interest. Additionally, some medications may have side effects that include loss of libido.
If you notice a decline in your libido, especially if it is sudden, consulting a doctor is advisable. The doctor can conduct tests to determine the underlying cause. Once identified, the doctor may be able to restore your sexual interest with appropriate treatment. For example, if the loss of libido is due to depression, psychological counseling or antidepressants might help. If it is due to low testosterone levels, testosterone replacement therapy can be considered. If a particular medication is the cause, the doctor may suggest an alternative medication.