There are a great many stereotypes associated with Catholicism - most people in England imagine Catholics to be mainly old women who kneel and say the rosary at a hundred miles an hour in front of a statue or other image, before getting out a few dozen prayer cards to as many different Saints and praying each in turn.
Whilst these stereotypes are not entirely undeserved, they are often badly misunderstood, and younger Catholics have, by and large, and for a fair number of years, concealed their faith from those around them; for fear of mockery or even derision. This is something I see every day in the Catholic school at which I work - there are those who are clearly nervous about coming into the chapel to say the rosary, or joining the school choir, or reading at mass; and this mentality is being carried through into young Catholic adults. So the stereotype of Catholics being old exists not because there aren't young Catholics, but because they are not as open about their faith.
So what might young Catholics (teenagers onward) do to show their faith? There are easy answers to this question; wear crucifixes or rosary bracelets, talk openly about their 'faith' behaviours (how many Catholic teenagers would omit mass when asked by a peer "what're you doing this weekend?") and discuss their faith openly when appropriate.
The more complex answer is that we must encourage the young to be active and effective witnesses in everything they do. Far from rubbing people's noses in the faith, this is perhaps an even more subtle change than those mentioned above. The outward signs are important, but they must support a fundamental change in our approach to life - to quote Blessed Teresa of Calcutta, "kindness has converted more people than zeal, science or eloquence"*
Of course these things are easy to suggest, but most teenagers are social animals, and will not want to be the one who initiates this change in their circle of friends - faith is, almost by definition, a personal experience and for many teenagers is hidden even from close friends. So how do we encourage the young laity to take up the outward signs of the faith? The great work of institutions such as Soli House and Alton Castle helps immensely, but the encouragement must stretch beyond a weekend's retreat into their scholastic and familial relationships too.
Social media is much condemned in education as a whole new way of bullying; and pupils are subjected to assembly after assembly about how poorly people behave on the Internet. Why should we not be encouraging the use of social media as a way to share their feelings? Indeed a perennial feature in those assemblies is how easy it is to be brave from behind a computer screen, to say something you might not if you were in front of the person; why not harness that to a positive - we should be encouraging young people to refer to their faith in their status updates, tweets and blogs.
I will finish with what may be the most controversial comment of this post: In my experience those young people who remain with and develop their understanding of their faith into and through their twenties are those individuals whose experiences or preferences (often both) of Catholicism are notably conservative. This is not to say they do not also embrace more modern church practices, but they have a distinctly old-fashioned approach to many areas which, whilst never officially changed, have developed into new practices by themselves. For example the practice of holding hands with the person next to you during the Our Father at mass - I know the use of the orans position for the laity is common in parts of the world, but the holding hands as far as I can tell is an entirely new innovation. I have seen some families doing this in mass, and I was encouraged to do it whilst at a Soli House-like retreat during secondary school, but I have never seen it done by a group of young people who have come to mass of their own volition. Even the tangible outward signs mentioned above are considered old fashioned, but it seems that it is those who do wear crucifixes and say the rosary who are most likely to remain with the church into their adult years.
* quote taken from a tweet by Ashley Kiczek - @1sistersR4ever