Would you prefer the age if the person to be across all reincarnations or can each one have their own age? You can have the age of a person to be shown at events, and if you don’t care about the total age you could number the incarnations like we number kings; Sebastian I, Sebastian Ⅳ, Sebastian Ⅷ, etc. I don’t think Aeon supports multiple start and end times for the same item (person, event, …).
Another idea is to have each incarnation as above, and all have a relationship to another person that represent the “complete” character – maybe that person’s “age” can be calculated. I don’t know how to configure the items properly for that to work.