I stopped doing this each time I used them when Mini Boo reached 1.
She still has milk in a bottle at bed time (she's now 22 months) but I only sterilize her bottles once a week now and that's mainly to rid them of that icky sour milk smell that never seems to disappear from washing them alone.
I was sterilising baby food equiment one day (I breastfed so didn't need to do bottles) and turned round to see darling daughter sitting there eating the cat food. I thought 'hmmmmmmm'. Later that day I took her into the garden & she took a fancy to the dirt..so the steriliser went into the cupboard!
im sure the "correct" time is 1 year, but I have four children and have always figured that if they are crawling and picking things up from the floor then why bother sterilising.... follow your instincts....