It all depends on his ability to make judgments. If he can decide for himself and is able to take care of himself then he is considered sober and in possession of his senses; as such, his testimony is valid.

 

The fact that he did not know all of the requirements and conditions does not absolve him from his essential duties. So, if he has been neglectful in the past, he should make up.

 

If he is unable to make up for all of them, he should ask forgiveness and compensate for them by doing whatever optional acts of charity that he is able to perform; he should also make a firm resolution never to neglect his essential duties again