Metafont is Donald Knuth's font description language supporting obscene numbers of parameters, including multiple weights ("asking an artist to become enough of a mathematician to understand how to write a font with 60 parameters is too much"). The most-widely-used Metafont font is Computer Modern, which, unsurprisingly, is Modern rather than old-style.
However, there are apparently some old-style Metafont fonts available. Looking through one old list (1997), I see one called Pandora described as "a little like Palatino", which is old-style. More information on this font: CTAN, LaTeX font catalogue.
See also http://www.math.utah.edu/~beebe/fonts/metafont.html, which lists some Metafont fonts, and the LaTeX font catalogue list of fonts (most probably not Metafont).
Gentium is definitely old-style, and its Gentium Basic variant comes in 4 weights (regular, book, bold, book bold), where the Book weights are slightly heavier:
The Basic fonts have a reduced character repertoire, but the project plans to support book weights for the entire font:
The main Gentium family will eventually have a complete matching Book weight, along with matching italics.
Our next major effort is completing bold and bold italic weights of Gentium Plus alongside a new Gentium Book Plus family. These new weights are currently available for Gentium Basic/Gentium Book Basic.")