I am so, so sorry for your loss. Gentle (((hugs))).
You did NOT do anything wrong. Sadly, miscarriages are not all that uncommon, although you usually don't hear much about them until one happens to you.
You are also NOT too old to try to have a baby. My third baby was born after I had been 31 for six months, and all three of my children have been born since I was 27 (one month away from 28). There are many women older than you who have children. (((hugs)))
It is normal to feel one way one minute and another way the next. Some of that is because of how your hormones are changing, and some of that is just because this is a traumatic time. There is no particular way you "should" be feeling, and no particular way you "should" handle your loss. For each woman, it is different.
I have had 2 losses, one in January 2006; the second was, in fact, on 3/15/11 (I think maybe your loss was more recent, on 5/15? Just this past Sunday? 3/15 was a Tuesday...a day I'll never forget.) My first loss was a blighted ovum, which means the egg was fertilized and the baby never grew. My recent loss...it was at 11 weeks 1 day, and we had already seen what appeared to be a healthy little baby on ultrasound at 8 weeks. On that day, my baby measured 11 weeks, but had no heartbeat...meaning we'd lost him or her in the previous 24 hours.
But I have had three healthy children born in between my two losses. Just because you have had one miscarriage, that doesn't mean you'll have one the next time you are pregnant - if and when you are emotionally ready to try again. Do not feel pressured to try again soon if you aren't ready, though. And likewise, if you ARE ready, do not feel like you haven't waited long enough...as I said before, the grieving process is different for every woman.
Sending you lots of love and prayers for healing and peace.