This article says he's 78.

Frank-Ronald Bischoff, who won a constituency seat, has admitted to working as a senior Stasi officer.

For 12 years, the 78-year-old worked covertly to subdue anti-communist protests in the dying days of the GDR and targeted citizens who applied to leave, according to local reports.

When confronted about his role in the secret police in 2017, he told Bild: “I do not comment on questions regarding the Stasi. I faithfully and conscientiously fulfilled my duties according to the laws of the GDR.”

Probably around 70 if he started working at 18.