Tujuan penelitian menganalisis penerapan hukum acara mahkamah konstitusi pada putusan nomor 90/puu-xxi/2023 tentang batas usia calon presiden dan calon wakil presiden republik Indonesia. Tipe penelitian yang digunakan dalam penelitian ini adalah metode penelitian hukum normatif. Hasil penelitian bahwa Proses pengujian perkara Nomor 90/PUU-XXI/2023 menimbulkan inkonsistensi terhadap hukum acara Mahkamah Konstitusi, antara lain pelaksanaan yang di daftarkan kemudian dicabut lalu ditarik kembali pendaftaranya, pengujian permohonan uji materil ke Mahkamah Konstitusi seharusnya diajukan sendiri oleh orang yang merasa dirugikan hak konstitusionalnya, adanya komflik kepentingan Ketua Mahkamah Konstitusi, dan pertimbangan hukum hakim Mahkamah Konstitusi yang berbeda dengan pertimbangan hukum dengan perkara-perkara yang ditolak meski dalil permohonanya sama. The research objective is to analyze the application of constitutional court procedural law in decision number 90/puu-xxi/2023 concerning the age limit for presidential and vice presidential candidates of the Republic of Indonesia. The type of research used in this research is the normative legal research method. The results of the research show that the process of reviewing case Number 90/PUU-XXI/2023 gives rise to inconsistencies in the procedural law of the Constitutional Court, including actions that are registered and then revoked and then withdrawn, the application for judicial review to the Constitutional Court should be submitted by the person who feels aggrieved. constitutional rights, the conflict of interests of the Chief Justice of the Constitutional Court, and the legal considerations of the Constitutional Court judges which are different from the legal considerations of cases that are rejected even though the arguments for the petition are the same.