What level do you need to be to participate in raid battles in Pokemon GO?
The level requirement is currently 25+. It was 35, then lowered to 31, then 28, and finally to 25 (where it currently is). This all happened in one day earlier this week.
(I am level 22, so I feel your pain. I am really hoping that they change it to be somewhere around 15+ or 20+.)
Currently the required trainer level for raids is 20.
Source (Twitter): @PokemonGoApp
Trainers level 20 and above: You can now participate in Raid Battles at a wide variety of Gyms around the world.