import re

pattern = r"\bD\s*\.\s*O\s*\.\s*B[^:]*:\s+(\d{1,2}\s*(?:JAN|NOV|OCT|DEC|J\s*u\s*n\s*e)(?:\s*\d){4})"

s = (" This is python to extract date\n"
            "D\n"
            ".O.B.\n"
            ": \n"
            "14 \n"
            "J\n"
            "u\n"
            "n\n"
            "e \n\n"
            "199\n"
            "1\n"
            "work in a team or as individual \n"
            "contributor.\n"
            "And Name is: Zon; DOB: 12/23/\n"
            "         1955  11/15/2014   11:53 AM")

res = [re.sub(r"\n+", "", s) for s in re.findall(pattern, s)]
print(res)