<p>One of the most appalling details related by witnesses of the violence in Paris on Friday night is that several of the killers could have been extremely young, possibly only 18, or even 15, years old. This image of teenagers  still of school age, wielding automatic weapons to kill scores of people  is deeply shocking.</p> <p>So far, the only attacker who has been fully identified was 29 years old, and it is unclear if the witnesses descriptions of other terrorists is accurate. But their apparent youth would fit an emerging picture of those attracted to Islamic States ideology and  perhaps more importantly  the twisted gangsta-jihadi lifestyle some believe it offers.</p> <p>One trend of recent years in Islamic militancy has been the shift from foreigners launching an attack in the west  such as the 9/11 attacks  to so-called homegrown extremists. We still dont know where all the Paris attackers came from, and this is hugely important in determining the nature of the threat going forward.</p> <aside class="element element-rich-link element--thumbnail"> <p> <span>Related: </span><a href="http://www.theguardian.com/world/2015/nov/15/police-question-paris-attacker-family">Police question Paris attacker's family as investigation widens</a> </p> </aside>  <p>But another trend is the youth of those involved in militancy. A decade ago in the UK, the presence of a schoolboy in an extremist network was seen as extraordinary. Many remarked on the presence of a 19-year-old among the suicide bombers who attacked London in 2005. Since then, however, teenage terrorists and fighters have become unexceptional. </p> <p>If it is often older militants who engage in violence in their home countries; the average age of Europeans heading to Syria to fight with Isis appears significantly lower than that of the volunteers who travelled to Afghanistan to train with the Taliban or al-Qaida. Hundreds are barely old enough to vote.</p> <p>Why is this? One reason is practical. Al-Qaida and most of its affiliates have always been based in remote places, such as western Pakistan, that are hard to reach, and harder to leave. You needed to be committed, connected and resourceful to get there, and be prepared not to come out. Communication was limited, food bad, accommodation worse, celibacy assured and the risk of capture, injury or death was high. MI5 overheard British volunteers who made it to Pakistan complaining of boredom and chronic stomach upsets. Such a journey was not something undertaken on the spur of the moment by an impulsive teenager and his friends.</p> <p>In contrast, taking part in what was famously described as a five-star jihad in Syria required much less commitment. Reaching and leaving the conflict zone has been, until recently, relatively easy. The suspected mastermind of a Belgian Isis-linked cell that plotted a complex attack earlier this year <a href="http://www.egmontinstitute.be/wp-content/uploads/2015/03/academia-egmont.papers.75_16x24.pdf">dubbed himself a terrorist tourist in a clip</a> found on his mobile phone. The internet works, allowing Skype calls home and real-time respect from peers on social media. </p> <aside class="element element-rich-link element--thumbnail"> <p> <span>Related: </span><a href="http://www.theguardian.com/world/2015/nov/15/paris-attacks-identities-of-victims-from-more-than-a-dozen-countries-emerge">Paris terror attacks: identities of victims from more than a dozen countries emerge</a> </p> </aside>  <p>Isis also appeals to teenagers in a way that al-Qaida, led by an ascetic, bespectacled 64-year-old does not. The older groups videos usually involve a lengthy monologue in Arabic reminding Muslims of their various jihadi duties and little else. Isis propaganda films targeting western teenagers comprise short clips resembling a <a href="http://www.washingtoninstitute.org/uploads/Documents/pubs/ResearchNote_20_Zelin.pdf">cross between a video game and a trailer for an action movie</a>. </p> <p>The propaganda also promises weapons, camaraderie and excitement. Publications such as the multilingual Isis magazine, Dabiq, emphasise sexual opportunity too, either through marriage to another volunteer or rape. All is relayed peer to peer by thousands of supporters, many of whom are extremely young themselves.</p>       <figure class="element element-video" data-canonical-url="http://www.theguardian.com/world/video/2014/nov/13/isis-leader-abu-bakr-al-baghdadi-video"            data-short-url="http://gu.com/p/43adx"                    data-show-ads="true"            data-video-id="2192455"            data-video-name="Who is Isis leader Abu Bakr al-Baghdadi? - video"            data-video-provider="guardian.co.uk"            data-video-poster="http://static.guim.co.uk/sys-images/Guardian/Pix/audio/video/2014/11/13/1415899675617/Abu-Bakr-al-Baghdadi-017.jpg"> <video data-media-id="gu-video-451845729" class="gu-video" controls="controls" poster="http://static.guim.co.uk/sys-images/Guardian/Pix/audio/video/2014/11/13/1415899675617/Abu-Bakr-al-Baghdadi-017.jpg"> <source src="http://cdn.theguardian.tv/mainwebsite/2014/11/13/141113Baghdadi-16x9.mp4"/><source src="http://cdn.theguardian.tv/3gp/small/2014/11/13/141113Baghdadi_3gpSml16x9.3gp"/><source src="http://cdn.theguardian.tv/3gp/large/2014/11/13/141113Baghdadi_3gpLg16x9.3gp"/><source src="http://cdn.theguardian.tv/HLS/2014/11/13/141113Baghdadi/141113Baghdadi.m3u8"/><source src="http://cdn.theguardian.tv/webM/2014/11/13/141113Baghdadi.webm"/> </video> <figcaption><a href="http://www.theguardian.com/world/video/2014/nov/13/isis-leader-abu-bakr-al-baghdadi-video"> Who is Isis leader Abu Bakr al-Baghdadi?</a></figcaption> </figure>   <p>Once inside Syria, or Isis, or another militant group or network, a new dynamic takes over. Volunteers are exposed to a new and very different environment. Some become hardened, conditioned, and eventually prepared to murder ordinary people on a Friday evening in a peaceful city in their homelands or elsewhere. Others do not. But what no one yet knows is what proportion of the thousands of young Europeans who have made their way to Syria or Iraq will return to take up arms to kill and maim. Further details of the identities of last weeks attackers will help answer this vital question.</p>