Given the age of Richard of York, one has to assume he would reign for around a decade as Life Expectancy was generally [for Nobility and Royals] around 60 in the late Middle Age/Early Renaissance. This make Edward IV to become King in 1470s, and he would be in his 30s. Provided he has no health trouble, Edward IV should potentially be able to rule for some 20-30 years: enough time to sire an heir, with high chances of said heir being of age when his father dies, especially if he married earlier.Elfwine said:OTL, Edward died "suddenly" at 41 (in 1483). That doesn't suggest shaky health.
Richard III to be would be 50 in 1461 (assuming he succeeds as quickly as his son did OTL), so Edward is probably not going to predecease his father.