How old do I have to be so I have to generate the money back?

How many Darkcoins can you mine approximate per day with this rig ( 4 x R9 270 )? I belive not enough and dont forget the costs of electricity!
I dont run 270s myself but the newest sgminers seem to pull ~2.1mh (YMMV) so @8.4mh you'd pull in approx 0.20291872 drk per
day at the current diff (4163.71557343).
So using those number (which will change constantly but to give you an idea) would set you @ 985.61 days to make the 200 dark back.