I work with teenagers, many of them vulnerable, my boss know what I do and its not seen as unprofessional. I work with my brother who talks about airsoft at work, and I try to keep it a little quiet as I do not want some of the young people knowing I have RIFs and am able to obtain them, but he says a lot which I find a little unprofessional.
However it turns out one of our young persons plays regularly at the same sites as us Not sure what boundries this crosses, but Its the same when I see my young people in bars locally. I ignore and leave. However I wont be leaving a skirmish, would just rather not highlight it at work and make it clear we did not plan to be there together as its perfectly legal for them to be there and a bit different to being in a bar with them.
And yes, whatever is posted online become public property pretty much and many industries will look to your online behaviour and perceptions as an accurate view of the person, WRONGLY.. Partly why I have hardly any online presence, no FB or twitter etc... My best mate nearly got the sack for a off the cuff remark about a suppliers Rep being an idiot and the company put 2 and 2 together and found him and he got in big trouble...
Whilst your hobbies are yours to have, it might be better to review how public your information is if your job is that strict..!!!