Jennifer Garner will play Miss Marple in a re-imagining of Agatha Christie's sleuth. But don't think for a minute Garner will break out the age-enhancing cosmetics. This is to be a more youthful take on the franchise, with Miss Marple being in her 30s.   Doesn't this basically make her a Nancy Drew?   I remember watching Miss Marple TV shows as a kid. Part of the fun is that she wasn't a hip prot…