With an S corporation election, you would have been required to have paid yourself a reasonable salary last year and it is too late for that to be accomplished (i.e., there was not withholding for income tax and FICA).
In addition, there are filing deadlines (the relevant form is Form 2553) and it does not appear as if you would meet them to elect for last year.
See https://www.irs.gov/instructions/i2553#idm139773190567344
With respect to late elections, it does not appear as if you would qualify for that either.
https://www.irs.gov/pub/irs-drop/rp-13-30.pdf
