LR and DaDane, it is a deep muddy swamp you both are wading in. Here is one example of valiant efforts to make some sort of sensible morbidity rate comparison between covid and flu. Read the update at the end of article, especially the update.
To get an estimate of overall IFR, one would need to know the numbers infected in each age group to go with the IFRs for each age group, which are as TD described.