I don't think that anyone approached the late onset of periods. I have 5 girls so here goes:
Recently I told my doctor that I had started my period when I was 15. She made the sigh I often hear when I mention this to doctors. She felt that it was unusually late. She furthermore went on to state that the age of onset has gone down in recent years, so that they expect the first period at 10 years old. That surprised me as my girls have been into their teens before having theirs. One of my girls is not a biological child and just started her period at 10 years of age. I had two of my adult children tested for celiac disease and the results were negative. One has very low ferritin level and I am still suspicious, but what can you do?