The total number of Spotify users (free and paid) was going to reach 6.2 million in the first quarter of 2018. The source also mentioned in the same article that 3.3 million of these expected users are paid users. This number is confirmed in a separate report, which stated that 52 percent of Spotify users in the Netherlands were subscribers. To compare these numbers: Spotify reported it had 159 million active users worldwide in 2017 with 70 million paying subscribers worldwide in January 2018.
Spotify does not release data on the demographics of its users in the Netherlands. The closest data available comes from a national survey on audio behavior published by NLO (Stichting Nationaal Luister Onderzoek). In the most recent survey, all respondents said they preferred to listen to radio as their main source of music. However, respondents aged 13-34 years old preferred to use a music service such as Spotify more than other age groups. Indeed, especially Millennials (defined by NLO aged 20-34 years old) seemed to use the streaming service. The average daily reach of music streaming was 24 percent for Millennials in the Netherlands, compared to 15 percent overall. The source additionally mentions that Millennials spent 202 minutes per day on audio, which is higher than the national average of 190 minutes per day.
Telecompaper mentions that Apple Music and Deezer had 1.1 million and 800,000 users respectively as of the first quarter of 2018. What is evident, though, is that the monthly reach of Spotify is higher than its competitors. In January 2017, roughly 20 percent of 13 to 34-year-olds visited Apple Music, compared to the 36 percent who visited Spotify. Another popular way of listening to music in the Netherlands is through YouTube. In a recent survey, roughly 66 percent of all respondents, indicated they watched music videos on YouTube. This includes the non-Millennial age groups, people older than 37 years. When it comes to just listening to music, Youtube is even mentioned as being used more often than Spotify.