Gouhou TS Ojisan no Ecchi de Midarana Seikatsu

Yuusuke Ojiyama, a perverted old man who's a DL erotic doujinshi artist, wakes up one morning to find himself transformed into a beautiful girl! It's a convenient disease called TS disease! Without going to the police or hospital, the old man quickly accepts the situation and enjoys his new girl body. He takes pictures of his body and masturbates... But since he's 37 years old, it's all legal!! Awesome! The old man's naughty and fun sex life begins!

(Source: DLSite, translated)