[6] At the age of 12, he joined the Beitar Jerusalem youth system, where he eventually also made his senior debut for the senior club of Beitar Jerusalem in an Israeli Premier League away match against Maccabi Tel Aviv, which ended in a 2–4 victory for his team; on 26 October 2015.

[16] On 25 June 2019, he signed with Israeli Premier League club Hapoel Be'er Sheva for five years.

[17] On 9 January 2024, Keltjens signed for Scottish Premiership side St Johnstone on a deal until the end of the season.

On 6 November 2016, Keltjens was first called up to the senior Israel national team, ahead of their match against Albania.

[19] On 24 March 2017, he made his senior international debut, coming on as a 60th minute substitute against Spain in a 2018 FIFA World Cup qualification (UEFA) away match that ended in a 2–4 defeat for his native Israel.