hiker (n.)youdaoicibaDictYouDict[hiker 词源字典]
1913, agent noun from hike (v.). Earlier as a type of boat:
The "hiker" or "tuck-up" as it is more generally termed, is a craft peculiar to the Delaware River, and is to the youth residing along the banks of that stream what the racing shell is to the Torontonian .... The origin of the name "hiker" is veiled in mystery. No member of the clubs engaged in sailing these boats can give anything like a satisfactory derivation of the word. The most common explanation is that it is corrupted from the local verb "to hike," which means to run or fly swiftly. ["Harper's Young People," 1885]
[hiker etymology, hiker origin, 英语词源]
youth (n.)youdaoicibaDictYouDict
Old English geoguð "youth; young people, junior warriors; young of cattle," related to geong "young," from Proto-Germanic *jugunthi- (cognates: Old Saxon juguth, Old Frisian jogethe, Middle Dutch joghet, Dutch jeugd, Old High German jugund, German Jugend, Gothic junda "youth"), from suffixed form of PIE root *yeu- "vital force, youthful vigor" (see young (adj.)) + Proto-Germanic abstract noun suffix *-itho (see -th (2)).

According to OED, the Proto-Germanic form apparently was altered from *juwunthiz by influence of its contrast, *dugunthiz "ability" (source of Old English duguð). In Middle English, the medial -g- became a yogh, which then disappeared.
They said that age was truth, and that the young
Marred with wild hopes the peace of slavery
[Shelley]