Unless you are a very dedicated and trained athlete, that is low. You should get it checked out right now - seriously.
That is still too low. You need to get it checked. I have been very physically active all of my life. College football (American football), then triathlete, and I still play competitive softball with guys half my age and less. At my peak I was at 46 rested. A slow heart rate can mean an enlarged heart, which isn't good.
i'm 54, runner and biker. resting pulse is usually 46-48. i agree with tonyt53