If your Half Elf is a Human with the Fey Blood trait you get to choose one Elven Common trait to represent his elven ancestry. By choosing Essence of the Earth your half elf becomes immortal! In that situation, the character should have to use the Ages of the Elves for stat development instead of the Ages of Man. This will tend to make half Elves physically weaker and mentally stronger then theIr human counterparts. Any Half Elf (regardless of burn) should bear the same stigma as the Bastard trait (1D Infamous) at least among Nobles and Etharch. They always count as different race for inconspicuous and disguise. They should be able to choose from both, Human and Elven life paths rather than having to choose one or the other. (As long as it fits their background and concept)
Using Elvish age for Mannish LP times is going to do weird things. Unless you’re taking huge numbers of Mannish LPs, you’re stuck in the first few of age categories. 7-9 mental, 13-14 physical. Time per LP loses most of its meaning. And you’re in the odd position of playing a callow immortal youth, but one wiser than Men… living among Men. I’d rather have immortality kick in at 25 using the Mannish chart, so your stats just stop at 7/16, but I don’t love that solution either.
Mixing LPs will break things. You get one stock or the other. Don’t try to put them together.
It’s fine to make half-Elves infamous, but that’s a world-building decision. BW is Tolkienic, and the Half-Elven there were great nobles themselves. Elrond certainly has great renown without blemish, and it’s not like he overcame great hardship or derision to get there.
That is true and in a tolkienic world it doesn’t make sense to do it that way. Perhaps they should be treated as if they had the Vitality of Youth trait to represent their immortality when halfelves have the essence of earth as part of their fey blood trait instead of using the elven aging chart. That way halfelves (7 Mental / 14 Physical). A little stronger than the average elven youth (7 Mental / 13 Physical), a lot smarter and stronger than the average human youth (11 - 14 years: 6 Mental / 13 Physical) to start with, but the humans would catch up quickly and even surpass the halfelves for a while before their inevitable decline and death. The elves, having pure blood, will continue to grow stronger in both mind and body, while the halfelves stand still.