John Louis of Nassau-Saarbrucken (1472-1545) was 72 when he expired.But the thing is no monarch back then (or at least I know of) made it into their late 70s, Philip made it to 71, so if you want you could make him live to 75. But any further is a bit out there.
Christian-August of the Palatinate-Sulzbach (1632-1708) was 75 at his end.
William IV of Henneberg-Schleusingen (1480-1559) was 78 when he died.
Bernard VII of Lippe (1429-1511) was over 80 when he passed.
Late 70s is long but not impossible given the contemporary rulers above, especially if fitness and semi-decent eating continue to be a part of Edward's life well into middle age or longer. Besides given how much the events of the Elizabethan and Tudor eras come to define England's history the impact of Edward ruling for those years will be disproportionate.