Here are a couple of options- both have a slight modification to your original table
\begin{tabular}{c||p{.2\textwidth}p{.2\textwidth}p{.2\textwidth}p{.2\textwidth}}
and I have broken a couple of lines in some of the cells- such manual tweaking is fairly typical when working with tables, especially in something as important as a beamer presentation.
Use makebox

Use resizebox

% arara: pdflatex
% !arara: indent: {overwrite: yes}
\documentclass{beamer}
\begin{document}
\begin{frame} {Original}
\begin{tabular}{c||cccc}
\hline
Variable & 0 & 1 & 2 & 3 \\ \hline \hline
Age & $<60$ & 60-79 & $> 80 $ & \\
Vitals & $P<100$, $ SBP>100$ & $P>100, SBP>100$ & $SBP<100$ & \\
Comorbidity & No major & & IHD, CCF, other major & Ranal, liver failure , malignancy \\ \hline
\end{tabular}
\end{frame}
\begin{frame}{Modification}
\makebox[\textwidth][c]{%
\begin{tabular}{c||p{.2\textwidth}p{.2\textwidth}p{.2\textwidth}p{.2\textwidth}}
\hline
Variable & 0 & 1 & 2 & 3 \\ \hline \hline
Age & $<60$ & 60-79 & $> 80 $ & \\
Vitals & $P<100$,\newline $ SBP>100$ & $P>100\newline SBP>100$ & $SBP<100$ & \\
Comorbidity & No major & & IHD, CCF, other major & Ranal, liver failure, malignancy \\ \hline
\end{tabular}
}
\end{frame}
\begin{frame}{Another modification}
\resizebox{\textwidth}{!}{%
\begin{tabular}{c||p{.2\textwidth}p{.2\textwidth}p{.2\textwidth}p{.2\textwidth}}
\hline
Variable & 0 & 1 & 2 & 3 \\ \hline \hline
Age & $<60$ & 60-79 & $> 80 $ & \\
Vitals & $P<100$,\newline $ SBP>100$ & $P>100\newline SBP>100$ & $SBP<100$ & \\
Comorbidity & No major & & IHD, CCF, other major & Ranal, liver failure, malignancy \\ \hline
\end{tabular}
}
\end{frame}
\end{document}
beamer" is presented in Including large tables in abeamerframe. – Werner Jan 26 '14 at 18:18