i dont usually pay attention to a li's age! the most important part is that he is attractive to me, either physically or personality-wise. though id be lying if i said i dont want more younger lis.. especially true shota;-;......
i think there is appeal in all kinds of ages. younger lis are cute and boyish (and when they hit you with a "im not a little boy anymore, oneechan" or "wait for me to grow up" oh my god.........), similar age feel like friends and its very nice, and older lis provide this sense of comfort and security and protection... and of course some maturity in the relationship ehehehe........
but that only counts if the writing is good. doesnt matter whether a li is 8 or 48. if the writing sucks (an older li acting like a whiny teenager or a teenager li acting like this wise old man with 80 years of life experience), im just gonna be frustrated either way! lol (though the second one is just so genuinely funny i cant bring myself to be mad)