Closure of coronal sutures starts at age of -

This question is tricky one. Most of the guides have given option c is the answer. Which is incorrect. Coronal suture is completely obliterated at 35-40 years. But, read the question carefully, examiner is asking when the closure starts (not completes). Closure of coronal, lambdoid and sagittal sutures starts at inner side at 25 years. And it is complete on outer side :- Sagittal suture → 30-35 years. Coronal suture → 35-40 years. Lambdoid suture →  45-50 years.