"A BFP uniformed personnel who has accumulated at least twenty (20) years satisfactory active service, regardless of age, may optionally retire and be entitled to one (1) rank higher than the permanent grade last held. Provided, that, he/she has served at least one (1) year of active service in permanent grade..." -RESOLUTION NO. 2001-01 Section 8.3.1
Please refer to this link for documentary requirements.