Source is arguably the best.
You need a computer that can run Half-Life 1From Wikipedia:System requirements Windows 95, 98 or NT; Pentium 133 (166+ recommended); 24 MBRAM (32 recommended); mouse; keyboard; 640x480 SVGA high color (16-bit) display; Windows-compatible sound device; 400 MB hard drive space; 3D accelerator card recommendedThis besides the obvious good internet connection, you will need a copy of Half-Life 1 installed because Counter Strike is a mod of it.
The recommended age to play Counter-Strike is typically around 16 years old, as the game features intense competition and may involve mature themes. However, the game has a rating of M for Mature by the ESRB, suggesting it's suitable for players aged 17 and older. Ultimately, parental discretion is advised, considering the individual maturity level of the player.
Da Strike was created on 1994-12-16.
The Hunger Strike was created on 2008-03-16.
Crime Strike - 1999 2011-12-16 was released on: USA: 16 December 2011
Crime Strike - 1999 2012-03-16 was released on: USA: 16 March 2012
Crime Strike - 1999 2012-04-16 was released on: USA: 16 April 2012
Crime Strike - 1999 2012-07-16 was released on: USA: 16 July 2012
Strike It Rich - 1951 1954-02-16 was released on: USA: 16 February 1954
Crime Strike - 1999 2013-09-16 was released on: USA: 16 September 2013
Crime Strike - 1999 2013-12-16 was released on: USA: 16 December 2013
Air Strike - 2004 V is rated/received certificates of: Germany:16 (cut) Iceland:16 Netherlands:16 Singapore:NC-16 USA:R