Section 44AD

As I understand, 44AD can be availed since the income does not exceed basic exemption limit.

Moreover, there is no compulsion to avail 44AD for continuous 5 years. However, if 44AD is not availed for 5 continuous years, then the assessee will not be eligible to avail 44AD for 5 years from the year in which the assessee opts out of 44AD.

You are absolutely right

Absolutely, he can opt sec 44AD presumptive taxation scheme in 2019-20.