Whether one is young, old, or on the verge of being a senior citizen, the drive to push the envelope rages.
講解：
one=a person
on the verge of ... 在...的邊緣 senior citizen 老人
drive 強烈的慾望
push the envelope 挑戰極限、超越自己
rage v. 肆虐 這裡的the drive to ... rages表示的就是“會有一種強烈的慾望做某事”
They love the adrenaline rush that comes with the act of participating in an extreme sport.
講解：
adrenaline rush 腎上腺素飆升、非常興奮的感覺
comes with ... 和...一同到來
the act of sth ...的行為
participate in sth 參加...
The world's biggest triathlon, the Ironman, consists of a 2.4-mile swim, followed by a 112-mile bike race, and finished off by a 26.2-mile run.
講解：
這句話是作者文章中的一個例子。作者想表達的是參加極限運動可以給人帶來極強的成就感（a great sense of accomplishment/achievement）並獲得別人的尊重（respect）
triathlon 三項全能運動 the Ironman 鐵人三項
consist of sth 由...組成
mile 英里
(be) followed by sth 由...緊隨其後、後面是...
bike race 自行車騎行
(be) finished off by ... 最終是...
