No fully long-established King of England lived to 70 until George II... but Edgar Aetheling whom Harold usurped died at 75, and Robert Curthose whom Henry I usurped died age 82. Between 1066 and 1727, the monarchs who died natural causes past age 60 were
- Edward the Confessor 63
- Henry I 67
- Henry III 65
- Edward I 68
- Edward III 64
- Elizabeth I 69
- James II 67
- George I 67
Natural deaths before 60 were:
- William the Bastard 59 (disputed - maybe accident)
- Stephen 58
- Henry II 56
- John 49
- Henry IV 45
- Henry V 35
- Edward IV 40
- Henry VII 52
- Henry VIII 55
- Edward VI 15
- Broody Mary 42
- James I 58
- Charles II 54
- Mary II 32
- Anne 49
So, an ancient English monarch was more likely to die before 60 than after 60 BUT he or she had better than one chance in three to live past 60. Actually since Harold was 44, he by definition was no longer going to die age 35, 40, 15, 42 or 32, so that makes 8 to 10 - Harold had about even chances to die before age 60 (year 1082) or after age 60.
It is perhaps something of a coincidence that the actual English rulers ended up including 8 who died between 60 and 69 but 0 who died past 69 - see the examples of Edgar and Robert. "At most" actually means that Harold living past 80 is the less likely option but nothing unrealistic.
How would Anglo-Saxon English society of 1102 handle an aged king, just past 80 (it had never happened before!) and his relations with his middle-aged sons and the generals who unlike him are physically vigorous?