Two people who have a lot in common and who share a lot of interests are an example of people who would be described as kindred spirits.
Origin of kindred
From American Heritage Dictionary of the English Language, 5th Edition
- From Middle English kindrede, alteration (with epenthetic d) of kinrede, cünreden (“kindred”), from Old English cynrēd, cynrǣden (“kindred, family, generation, posterity, stock, species”), from cynn (“kind, sort, quality, race, family, rank, gender”) + -rǣden (“condition, state”), equivalent to kin + -red. More at kin.