Bulletproof vests are legal and, according to the Weapons Act, are not a weapon but protective equipment. Every German citizen is entitled to purchase and wear this form of protection. Age plays a minor role. Wearing a bulletproof vest is also permitted in Germany, but it cannot be worn at demonstrations or other public events. If you wear a bulletproof vest at a demonstration, for example, you are violating the assembly law.
According to § 17a, the Assembly Act states, < https://dejure.org/gesetze/VersG/17a.html > that it is forbidden to use protective weapons or objects that are suitable as protective weapons in the open air, in elevators or other public events or on the way there and to ward off enforcement measures by a holder of sovereign powers.
This law implies that no protective weapons may be carried at demonstrations and gatherings. Protective weapons are passive weapons that are intended exclusively for the protection of people. This also includes protective vests. You can prevent authorities from making access. That means a bulletproof vest would prevent the police from striking down a citizen with a firearm in an emergency.