You really must ask the company why they have refused.
They will have refused because he does not score enough points to be considered a good risk - maybe he smoked, or still does, or drinks more than the limit - it could be an accumulation of many factors. It could simply be that his age and weight are not acceptable to this company.
Whenever you apply for insurance you are always asked if you have been refused before. Please do not be tempted to lie - as you will probably be found out.