Vertical alignment of nested table

I have two tables nested inside of a larger table. One of the nested tables is taller than the other, and I'd like to have the two tables line up together at the bottom. I've tried inserting [b] in the outer table, and I've tried declaring the outer table's column containing the shorter inner table as b{0.25\textwidth} instead of l. Neither of these worked. I'm pretty new to LaTeX, so maybe there's something basic that I'm missing.

Here is a minimal version of what I'm working with:

\documentclass{article}
\usepackage{array}
\newcolumntype{C}[1]{>{\centering\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}
\begin{document}

\begin{tabular*}{0.5\textwidth}{@{\extracolsep{\fill}}ll}
A & B \\
\begin{tabular}{rC{5em}}
aaa & 1 \\
bbb & 2 \\
ccc & 3 \\
ddd & 4 \\
eee & 5 \\
fff & 6 \\
\end{tabular} &
\begin{tabular}[b]{rC{5em}}
ddd & 4 \\
eee & 5 \\
fff & 6 \\
\end{tabular} \\
\end{tabular*}

\end{document}


This is what my code is giving me:

But I'd like to have something like this:

The alignment specifier for a tabular could be considered an "anchor point". Use [b] for both the inner tabulars:

\documentclass{article}
\usepackage{array}% http://ctan.org/pkg/array
\newcolumntype{C}[1]{>{\centering\let\newline\\\arraybackslash\hspace{0pt}}m{#1}}
\begin{document}

\begin{tabular*}{0.5\textwidth}{@{\extracolsep{\fill}}ll}
A & B \\
\begin{tabular}[b]{rC{5em}}
aaa & 1 \\ bbb & 2 \\ ccc & 3 \\ ddd & 4 \\ eee & 5 \\ fff & 6
\end{tabular} &
\begin{tabular}[b]{rC{5em}}
ddd & 4 \\ eee & 5 \\ fff & 6
\end{tabular} \\
\end{tabular*}

\end{document}