Over on the Living History Forum there's a discussion of how various re-enactors got started with this - well, more than a hobby and more like a way of life. For some it seems to be a fascination with swords, or the Sharpe novels, or playing on World War Two tanks as a child.
For me, it started with a Viking on a bus.
I was eleven, and on holiday on the Isle of Man. Every year, they hold a big Viking Festival in Peel, complete with longship races across the bay (yes, they have more than one!). My family were staying in Douglas, so we got the bus across the island to see what it was all about.
Sitting on the bus in front of me, so close I could have reached out to touch the fur on his collar if I'd dared, was one of the Vikings, in his costume, with his shield and weapons.
Looking back on it, his kit owed more to Hollywood than historical research, but I was hooked. I wanted to be the sort of person who dressed in costume, on the bus.
When I got to university, studying history and archaeology, the only re-enactment group on campus was the Sealed Knot. They were a division of Gilbert de Haughton's regiment, Royalists, and I went to pike drill behind the halls of residence, and climbed up Pendle Hill on Hallowe'en looking for witches to burn, and shouted "The King and the Cause" at the Battle of Nantwich - which terrified the life out of me. It was a big battle, with cannon, and there I was, in the middle of a pike push (which is like a rugby scrum with added sixteen foot long poles), with my helmet askew.
The following year, I joined the Gilbert and Sullivan society instead, and became a fairy in Iolanthe!
There was still something about re-enactment that attracted me, though, so when the grandson of the lady I was working for was going through problems at school, I suggested re-enactment to get him away from the computer and out in the open air, with interesting people and things to do. He was interested in history, so that was a good start. I found a local medieval group, brushed up my rusty sewing skills to make the kit, and off we went.
The lad dropped out after a season or so, having discovered an interest in archery, which he could do with his grandad locally, and I stayed on, learned spinning and weaving, and basic swordplay, to go with my knowledge of the history and archaeology of the period - and I've been doing it ever since.
And whenever I get the chance, I travel on the bus or train in kit. You never know when an impressionable child might be watching, and be inspired for life!