Unfortunatly there is no filter  for [Today] - 30 (would be nice) What I
do as a work around is in the list  that you want to filter for 30 Days
create a new column called Filter 30 Days or something like that. Make
this a calculated list. Give the column a simple description, and in the
Fomula box  enter =Created+30 and choose the Date and Time format and
Date Only (I also clear the Add to default view).

Then create a new view  setting up a filter to show  "Filter 30 Days - is
greater than or equal to - [Today]

I hope this helps. If there is a better way please please share.