Probably the single biggest determinant in whether or not you are fit enough to climb Mont Blanc. Look at the chart on the left:
of the 2000 clients we have had to date, the vast majority that made the summit would have fitted one of the first three categories above. At most 50% of those from category 4 made it, and these were usually people with a solid background in endurance sports who had by their own definition "let themselves go a bit".
The rare clients we have had from category 5 have virtually never made it, and most have dropped out of the course in the early stages. We do not prejudge on appearances and if you do reasonably well on the first three days on Gran Paradiso we will be happy to try Mont Blanc with you regardless of body shape. However getting yourself into or below category 3 on our chart is probably the single biggest thing you can do to improve your chances.