Abstract: Using highly cited scientists in the fields of molecular biology & genetics and physics as a case study, the age distribution at the time of publication for these scientists (so called the publication age distribution) is studied through normal and fractional counting. The data show that these scientists publishing their most articles are mainly at the age between 40 and 55 (so called middle age). The publication age distribution for older highly citedscientific group and individual scientist in five research fields are observed and analyzed respectively. Key words: highly cited scientist; productivity of scientific paper; age