There are varying definitions in this community. 

This is the Official GYO formula:

• Younger age is Y, Older is Z
• Formula: 4/3Y ≤ Z
• Younger = 18, 1.333… * 18 <= Z, Older >= 24
• Younger = 30, 1.333… * 30 <= Z, Older >= 40
• Younger = 38, 1.333… * 38 <= Z, Older >= 50.6

The GYO community is sympathetic to the smaller age differences when partners are younger. As partners age, differences in age become less societally significant so a larger age gap is needed to qualify as a GYO relationship.

The perception of age difference changing as we get older just shows how arbitrary age really is.

Younger Age Range	Older’s Lower Limit	Couple’s Age Difference	Older’s years to 100
18	24.00	6.00	76.00
19	25.33	6.33	74.67
21	28.00	7.00	72.00
23	30.67	7.67	69.33

Younger Age Range	Older’s Lower Limit	Couple’s Age Difference	Older’s years to 100
25	33.33	8.33	66.67
27	36.00	9.00	64.00
29	38.67	9.67	61.33

Younger Age Range	Older’s Lower Limit	Couple’s Age Difference	Older’s years to 100
40	53.33	13.33	46.67
42	56.00	14.00	44.00
44	58.67	14.67	41.33

Attraction defined:

• Teleiophilia – Sexually mature young adults, 18 – late 30s
• Mesophilia – Middle aged adults, 40s – late 50s
• Genontophilia – Old adults, 60+

Thanks to /u/justaguy0021 for the formula optimization and proof. https://imgur.com/qZnuPZA

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