Hi.
If you need to retrieve an extermum several time, I suggest you use a sorted data structure.
Also, instead of returning the found_maximum and the name, you could return the index, allowing to retrieve any information. And handling the case where the table is empty:
function find_maximum(table)
local m = nil
for key, item in pairs(table) do
if (m==nil or item[5]>table[m][5]) then
m = key
end
end
return m
end