Will and catherine having children in thier 40s-a good idea?

it appears to be a probability prince william ie duke of cambridge might be in his 50s when ascending the throne..with a long lived great granny and grandparents in good health as they get up there in years..having an heir in their 40s would possibly break this middle age and elderly ascending the throne..a good idea to wait a spell?..looking at a paunchy and premature looking and acting prince albert of Monaco..is this the trend?