"are allowed" is correct and usable in written English. You can use it when you want to express that someone has permission to do something. Example: Only people aged 18 and over are allowed to purchase alcohol.
Small dogs are allowed.
No upgrades are allowed.
Those payments are allowed.
Dogs are allowed.
Still, jeans are allowed.
Campfires are allowed too".
No pets are allowed.
Few advocacy groups are allowed.
No other chemicals are allowed.
Running and conditioning are allowed.
(Major leaguers are allowed eight).
Thanks to Ludwig my first paper got accepted! The editor wrote me that my manuscript was well-written
Listya Utami K.
PhD Student in Biology, Bandung Institute of Technology, Indonesia