I feel like it is important to point out that Steam does not require games to have any DRM. Not even Steam's DRM. It's entirely up to the game developer and/or publisher. Many games on Steam are already DRM-free where you can just back up the files and play without Steam.
I basically did that, bought AoE several times, back then on CD and again on Steam. First I used virtual drives with ISO images and later a cracked version.
Today I am only using the Steam version though because I can easily join multiplayer games with friends all over the world. Also, I really like all the additional features in the remakes of AoE that you can get on Steam.
Does this apply to AoE? I never played it much in its hey-day but it would be interesting to get into properly. I have no interest in buying an old game with DRM given the obvious potential for maintenance issues though.