BMI is a starting point but so many other things come into play... interesting quote from a clinical Endocrinology study:
Conclusions: Increasing paternal age at childbirth is associated with a more favourable phenotype in their children (taller and slimmer, with better insulin sensitivity in girls) but with a less favourable lipid profile.
So even though BMI is lower, the LDL/HDL profile is less healthy...
Here's the whole article if anyone is interested
This site is a Health Professionals' Continuing Education site.
Quick quote - sorry but it is quite 'scientific' in language - but extremely interesting nonetheless.
"As paternal age at childbirth increased, their children displayed a reduction in BMI and truncal fat. As BMI in childhood is predictive of adult BMI, our findings suggest that the slimmer children of older fathers may have a lower risk of obesity in adulthood. Increased truncal fat is a component of the metabolic syndrome, so that the children born to fathers aged over 30 years may be at a lower risk of metabolic disease and obesity. Importantly, the observed improvement in insulin sensitivity seen among girls born of older fathers would support this hypothesis, as a reduction in insulin sensitivity is predictive of the metabolic syndrome in adulthood. Nonetheless, there are conflicting reports regarding the effects of paternal age at childbirth on offspring obesity. In contrast to our study, a recent large investigation found an increased risk of obesity in young adult offspring in association with increasing paternal age. However, this was only observed when groups at the extreme of the paternal age spectrum were compared (<20 vs >50 years). Furthermore, unlike our study, they only examined males and parental BMI was not accounted for in their analyses to correct for genetically determined obesity.
However, increasing paternal age at childbirth was also associated with less favourable lipid profiles in their children. Specifically, children of fathers over 30 years of age had higher total cholesterol to HDL-C ratios compared with the children of younger fathers. Childhood lipid profiles worsened as paternal age at childbirth increased further, so that the children of fathers aged over 35 years had higher total cholesterol (due to higher LDL-C concentrations) than children of fathers aged ≤35 years. Childhood lipid profiles track or accentuate into adulthood. It is therefore possible that the less favourable lipid profiles in these children may deteriorate further later in life, placing them at a greater risk of cardiovascular disease in adulthood."