He was pretty poor at the World Cup, Spain game aside. He scored against Australia but was rather anonymous other than that, in the knockouts he struggled (the whole Netherlands team only scored 2 goals, both late against Mexico between Last 16 and 3rd place game).
I respectfully disagree. He scored 4 goals this World Cup, coming out of the "group of death", made an absolute mockery of one of the strongest Spanish sides in history, all while playing for a very mediocore side. Compare his World Cup goal scoring record to Cristiano Ronaldo or Lionel Messi, if you want to have a good laugh. It's interesting that people are willing to forgive Ronaldo's performances at the international stage, e.g., "he's out of form" or "coming back from injury", yet just a few short months after RVP manages to score MORE than Ronaldo and the same as Messi, who was playing with far better teammates, people are writing RVP off. Don't forget, RVP also scored against and defeated a very talented Brazil team to lead his team to 3rd place in the World Cup, coming from a team that is carried completely by RVP and Robben. Hardly a "poor" performance.
This excerpt really says it all (that RVP is continuing to perform at the highest level):
Van Persie ended the 2014 FIFA World Cup qualification campaign as top scorer in the UEFA section with 11 goals. In June 2013, he was appointed captain of the Dutch national team by manager Louis van Gaal. On 11 October 2013, he became the Netherlands' top goalscorer of all-time in an 8–1 defeat of Hungary, the Dutch's penultimate Group D match, where he scored a hat-trick. This put him on 41 goals in 80 internationals, surpassing the record previously held by Patrick Kluivert.
In the team's opening match of the 2014 FIFA World Cup, Van Persie captained the Netherlands to a 5–1 win over champions Spain in Salvador. He scored twice in the match, one of which was a flying header which was later nominated for FIFA Puskás Award for the most beautiful goal of the year. He was also named man of the match by FIFA. On 18 June, he scored his third goal of the tournament in a 3–2 defeat of Australia, a result that qualified the Netherlands to the knockout stage with one group match remaining.
In the quarter-final, Van Persie scored the Netherlands' first kick in a 4–3 penalty shootout defeat of Costa Rica. He scored his fourth goal of the tournament from a penalty kick in a 3–0 win against Brazil in the third-place play-off.
And the age thing really is overblown. RVP never relied on his pace, but more on his clinical finishing and vision and movement. Look at Drogba - he is very old now, but he still has that killer instinct to score goals.