Has anyone ever heard of "the 25% either way rule"?

I never have, and it's not sourced in any way on Wikipedia.

I love Wikipedia.

"25% either way" isn't even internally consistent - the range up has to be larger than the range down (25% down would mean 33% up, for example) for the rule to be consistent.

Before anyone AFDs it, you can dig up sources for this. And yeah, heard of it.

Not to mention kinda bizarre - by this logic an 18 year old could date a 13 year old.

LOL. I had heard of both the +7 and the 25% thing before--I really had. But like just said above, I never bothered to work out the math. Half +7:

You Them
14 14
15 14.5
16 15
17 15.5
18 16
19 16.5
20 17
21 17.5
22 18
23 18.5
24 19
25 19.5
26 20
27 20.5
28 21
29 21.5
30 22
31 22.5
32 23
33 23.5
34 24
35 24.5
36 25
37 25.5
38 26
39 26.5
40 27
41 27.5
42 28
43 28.5
44 29
45 29.5
46 30
47 30.5
48 31
49 31.5
50 32
51 32.5
52 33
53 33.5
54 34
55 34.5
56 35
57 35.5
58 36
59 36.5
60 37
61 37.5
62 38
63 38.5
64 39
65 39.5
66 40
67 40.5
68 41
69 41.5
70 42
71 42.5
72 43
73 43.5
74 44
75 44.5
76 45
77 45.5
78 46
79 46.5
80 47
81 47.5
82 48
83 48.5
84 49
85 49.5
86 50
87 50.5
88 51
89 51.5
90 52
91 52.5
92 53
93 53.5
94 54
95 54.5
96 55
97 55.5
98 56
99 56.5
100 57


25% either way, lol:

You Them, -25% Them, +25%
14 10.5 18.4
15 11.3 19.7
16 12.0 21.0
17 12.8 22.3
18 13.5 23.6
19 14.3 24.9
20 15.0 26.3
21 15.8 27.6
22 16.5 28.9
23 17.3 30.2
24 18.0 31.5
25 18.8 32.8
26 19.5 34.1
27 20.3 35.4
28 21.0 36.8
29 21.8 38.1
30 22.5 39.4
31 23.3 40.7
32 24.0 42.0
33 24.8 43.3
34 25.5 44.6
35 26.3 45.9
36 27.0 47.3
37 27.8 48.6
38 28.5 49.9
39 29.3 51.2
40 30.0 52.5
41 30.8 53.8
42 31.5 55.1
43 32.3 56.4
44 33.0 57.8
45 33.8 59.1
46 34.5 60.4
47 35.3 61.7
48 36.0 63.0
49 36.8 64.3
50 37.5 65.6
51 38.3 66.9
52 39.0 68.3
53 39.8 69.6
54 40.5 70.9
55 41.3 72.2
56 42.0 73.5
57 42.8 74.8
58 43.5 76.1
59 44.3 77.4
60 45.0 78.8
61 45.8 80.1
62 46.5 81.4
63 47.3 82.7
64 48.0 84.0
65 48.8 85.3
66 49.5 86.6
67 50.3 87.9
68 51.0 89.3
69 51.8 90.6
70 52.5 91.9
71 53.3 93.2
72 54.0 94.5
73 54.8 95.8
74 55.5 97.1
75 56.3 98.4
76 57.0 99.8
77 57.8 101.1
78 58.5 102.4
79 59.3 103.7
80 60.0 105.0
81 60.8 106.3
82 61.5 107.6
83 62.3 108.9
84 63.0 110.3
85 63.8 111.6
86 64.5 112.9
87 65.3 114.2
88 66.0 115.5
89 66.8 116.8
90 67.5 118.1
91 68.3 119.4
92 69.0 120.8
93 69.8 122.1
94 70.5 123.4
95 71.3 124.7
96 72.0 126.0
97 72.8 127.3
98 73.5 128.6
99 74.3 129.9
100 75.0 131.3

Based on the example given in the text, I suspect it's an attempt to rectify a perceived deficiency in that it doesn't allow 18/24. Possibly by someone who is in such a relationship and is thinking too hard about it, and hasn't thought through the other consequences of the rule.

IP account proxying for a banned user.