#!/bin/bash
s="Section1
    George, 1998-1995
     Peter, 1999-1990
     Simon, 1988-1960
Section2
     Gery,  2019-2015
     John,  1984-1983
     Thomson,  1978-1965"
sed --posix -n '/^Section1$/ , /^Section[0-9]*$/{:a;h;n;/^Section[0-9]*$/!ba;x;s/^[ \t]*//;p}' <<< "$s"