To cite package ‘RNAAgeCalc’ in publications use:

  Ren, X., & Kuan, P. F. (2020). RNAAgeCalc: A multi-tissue
  transcriptional age calculator. PloS one, 15(8), e0237006.
  https://doi.org/10.1371/journal.pone.0237006

A BibTeX entry for LaTeX users is

  @Article{,
    title = {RNAAgeCalc: A multi-tissue transcriptional age calculators},
    author = {Xu Ren and Pei Fen Kuan},
    year = {2020},
    journal = {PLOS ONE},
    doi = {10.1371/journal.pone.0237006},
    volume = {15},
    number = {8},
    pages = {-20},
  }