Wanga's Father, Frank Wetende, is a former A.F.C. Leopards and Kisumu Posta footballer who also played for the national team in the 1970s and early 1980s. His mother is named Noel Ayieta. He has three siblings, Richard Malaki, Nancy Kuboka and Magdalene Amboko, who is deceased.
In 2005, he joined Kisumu-based Lolwe FC, then playing in Nationwide League, the second tier football league in Kenya. He only stayed three months though, because the Nationwide was being revamped and thus closed. He was set to join Agro-Chemical, but the move did not happen as he was threatened by Agro players fearing for their place in the team, according to Wanga. He then went home and was persuaded by his mother Noel, to join the army. He failed the army test, and got a chance at Sher Karuturi, another Kenyan top-flight club. After waiting for a contract offer, his brother Richard called him over a job offer in Canada, and Allan joined his brother in Nairobi but it did not materialise.
After almost a year without a club, Lowle contacted him in late 2006 and he returned, but was picked up by Premier League club Tusker F.C., in early 2007. He played for Tusker until the end of 2007 season, when his club won the league. He managed to score 13 goals in his nine last matches for Tusker FC and 21 in total.
On 2 December 2010, he signed a contract with Hoàng Anh Gia Lai in the Vietnamese Super League.
Wanga married Brenda Mulinya, a Kenyan TV reporter on 3 September 2011.
At the beginning of the 2012 Kenyan Premier League, Wanga signed a loan deal with A.F.C. Leopards until 11 November 2012. At the end of the season, Wanga sealed a permanent move to Ingwe.
In January 2013, Wanga joined Floribert Ndayisaba in going on trial with Omani side Al-Nasr.
On 4 June 2014, Wanga agreed to a one-year contract with the Sudanese giants Al-Merrikh.
On 21 July 2015, Wanga agreed to a one-year contract with the Tanzanian club Azam FC. His first goal came in a Vodacom Premier League match against Stand United, During his one-year stay at Azam he was restricted to 11 appearances due to personal issues scoring 3 goals in the process.
In June 2016, Wanga completed a move back to his former side Tusker. On 17 July 2016, he played his first match back for the club in a 2–2 draw against Chemelil Sugar, coming on as a substitute for Michael Khamati in the 59th minute. He scored 4 minutes into injury time to put his side 2–1 up before having his goal cancelled out by Hillary Echesa a minute later.