Can I file N_400 as LPR for 5 years if I am currently separated from my US wife and can I file after 5 years anniversary too?

Generally, a Permanent Resident may become eligible to file a Form N-400 Application to become a naturalized citizen five years after first getting his "Green Card" (and actually may file 90 days before that threshold date). If the Permanent Resident originally attained his "Green Card" through a marriage-based application, and the marriage has since terminated, he may expect the USCIS to inquire about the marriage at his naturalization interview and examination. Depending upon the circumstances, the applicant should be prepared with information and documentation showing that the couple had lived together in a bona fide marriage notwithstanding its eventual termination, in order to persuade the USCIS adjudicating officer that he did not get his "Green Card" through fraud. Especially if your marriage may have become terminated fairly soon after you became a Permanent Resident, it would be wise to engage an immigration attorney for representation in the naturalization process. Some immigration law firms, including mine, offer legal services on a "flat fee" basis so that a client will know the total expense from the very beginning, and a few immigration law firms, including mine, offer an initial consultation free of charge.

Yes, you can.