Maybe I didn't explain myself well. None of the above seem to work for what I need. I needed the row number of the last row in a single column that had a check mark in it. After more research I found this that works exactly as needed.
=SUMPRODUCT(MAX((B6:B41<>"")*ROW(B6:B41)))
As used in the complete formula:
=IF(SUMPRODUCT(MAX((B6:B41<>"")*ROW(B6:B41)))>0,DATEDIF(INDIRECT("A"&SUMPRODUCT(MAX((B6:B41<>"")*ROW(B6:B41)))),TODAY(),"D"),"")
The other formulas either gave me the first row number which was empty or the very last row in the range. I want to thank all for trying. Sorry I didn't explain it better.