You can use \setstretch{..} to set a different factor, although in general changing the baseline from the one intended in the font design usually doesn't lead to an improvement.
Other comments, you loaded the geometry package (usually the best way of setting page dimensions) but then over-rode all its settings by setting lower level LaTeX parameters:
\oddsidemargin=0.0in
\evensidemargin=0.0in
\textwidth=6.5in
\marginparwidth=0.5in
\headheight=0pt
\headsep=0pt
\textheight=9.0in
\centerline{\huge \bf My Name}
\vspace{2.5pt}
\centerline and \bf shouldn't really be used in LaTeX they are hang overs from plain TeX (\bf is not even defined by default, just added as a compatibility layer by the document class). Whenever you have a font size change it is best to include a paragraph end (\par or blank line) within the same scope, otherwise you set large text on a small baseline.
Similarly
\noindent{\LARGE \bf Education} \\
Avoid \\ except in tabular etc. This should be
{\LARGE\textbf{Education}\par}
\line is only intended fro picture mode, I was surprised it didn't give an explicit error here but apparently not. Use \rule
{\line(1,0){475}}
Should be
\noindent\rule{\textwidth}{.4pt}\par
Or to change the width and colour
add
\usepackage{color}
then
\noindent\textcolor{red}{\rule{\textwidth}{5pt}}\par
I took the liberty to write up an answer, making your very large
example into a minimal one. As @cgnieder stated in the comments,
package scrlayer-scrpage defines an interface for defining page
headers and footer; mostly compatible with scrpage2. Mostly,
what does that mean? You received a warning, telling you that the
command deftripstyle is deprecated. True, it is. But it gives
you an alternative, and looking into the KOMA-documentation reveals:
You can just change the command name. But using this is not
recommended any more and is just there for compatibility reasons.
Is there any reason for making the document look like the
standard W0rd stuff? You should also consider using the class
scrreprt. @cgnieder made you aware of some other oddities in
the comments.
Be careful, you are loading packages twice.
\documentclass{scrreprt}
\usepackage{blindtext}
\usepackage{xcolor}
\usepackage[headsepline,automark]{scrlayer-scrpage}
\addtokomafont{headsepline}{\color{blue}}
\KOMAoptions{headsepline=10pt:\textwidth}
\renewcommand{\headfont}{\color{blue}\normalfont\slshape}
\newcommand{\versiondate}{\today}
\deftriplepagestyle{draftpages}[5pt]
{\versiondate}{\headmark}{}
{Draft}{\pagemark}{}
\begin{document}
\blinddocument
\clearpage
\pagestyle{draftpages}
\blinddocument
\end{document}
Best Answer
The following MWE gives red, 5pt line on page one and two:
See page 226 and page 54 in the KOMA-script manual (v3.18).