Alemán was born in San José, Costa Rica and then moved to Brampton, Ontario when he was 10. He attended St. Edmund Campion Secondary School. Keven started playing with Brampton A as soon as he moved to Brampton. Before joining Toronto FC, he played on the Under 16 Ontario Provincial Team coached by Patrick Tobo which also featured fellow players Bryce Alderson and Quillan Roberts. After the Provincial team he joined the TFC Academy in the Canadian Soccer League. Alemán showed great promise along with other Canadians Michael Petrasso and Dylan Carreiro, however all three players left over various issues with Aron Winter, the club's manager at the time. Before leaving to go on trial in Europe, Keven had his rights traded by Toronto FC to the Vancouver Whitecaps in return for Terry Dunfield. However, after a successful trial period in 2011 and attaining his visa, Alemán was able to join the youth ranks at Real Valladolid in Spain.
Herediano
In August 2014, Alemán left Real Valladolid to join C.S. Herediano of Costa Rica. He was unveiled by the team on August 7 with fellow signee Antonio Pedroza. He debuted for Herediano on September 11 in a friendly, and scored a goal for the side in a 3–1 victory. Alemán made his league debut more than two months later on November 30 in a 1–0 victory over Santos de Guápiles. Alemán was loaned out to fellow Costa Rican side Belén in January 2015, for the remainder of the season. He made his debut for the team against Carmelita on January 2. He scored his first goal for Belén against Limón in a 1–4 loss on February 14.
Belén
In July 2016, Aleman transferred to Belén, in order to accommodate his request for more playing time.
In December 2016, it was announced that Aleman had signed a 2.5 year contract with Saprissa. In January 2018, it was announced that Aleman had left the club after one year.
Alemán was eligible for both Costa Rica and Canada. He began with numerous training camps with Sean Flemming's U17 Canadian side in April 2011 and eventually became a large part of the group leading through the Concacaf championship onto the World Cup. He was a part of Canada's U17 soccer team, making his debut in the 2011 FIFA U-17 World Cup. He was also a part of Canada's 2013 CONCACAF U-20 Championship team. Alemán would later reveal to media that Jorge Luis Pinto had approached him about representing Costa Rica in December 2012, a month before the U-20 tournament. He declined, stating he was committed to the Canadian program. On June 27, 2013 Alemán was listed as a part of the confirmed 23-man squad for Colin Miller's Canada squad for 2013 CONCACAF Gold Cup. Alemán made his senior debut for Canada against Mexico July 11 as a second-half substitute for Kyle Bekker, the game ended in a 2–0 defeat. After more than three years out of the national team picture, Alemán returned to the side under coach Octavio Zambrano, appearing in a 1–0 defeat to El Salvador on October 8, 2017.
