Is it permissible to approach the ruler (wali al-amr) to request an extension of one's age for retirement, without resorting to the medical committee, and is this act forbidden (haram)?

The conduct you described is governed by the regulations of the company you work for. If the medical committee accurately and objectively assesses the applicant's age, then it is permissible to apply for retirement through them. This applies to those who are uncertain about their age. As for those who are certain of their age, it is not permissible for them to do so, as it constitutes deception and falsehood. It is also not permissible to petition the authorities to artificially inflate one's age, as this violates retirement laws and the Prophetic saying: "Muslims are bound by their conditions."