 Pari gbolohun yii: Ọmọ ìlú Needham, Massachusetts, Arnold lọ sí ilé-ẹkọ gíga, ó sì gbá hockey ní ilé-ẹkọ Noble and Greenough School àti ilé-ẹkọ Boston Junior Bruins kí ó tó darapọ mọ USA Hockey National Team Development Program fún sáà 200910. Ni ipele U-17, Arnold jẹ olori ẹgbẹ ti ẹgbẹ ti o yan ti o kopa ninu idije orilẹ-ede marun kan ni Slovakia; a pe ni oṣere ti o niyelori julọ ti idije naa. Níbi tí : 2010 IIHF World U18 Championships, Arnold ṣe igbasilẹ awọn aaye mẹta ni awọn ere mẹfa bi National Team Development Program, ti o ṣe aṣoju fun Orilẹ Amẹrika, gba ami ẹyẹ goolu. Ní ọdún 2010 National Hockey League NHL Entry Draft, Arnold ni a yàn ní ìpele kẹrin, 108th overall, nipasẹ Calgary Flames. 