I find that sometimes it is very easy to differentiate the more worldly-wise (which isn't always correalated with age) from the naive (which isn't always correated with youth), based on the knowledge apparent from the post. But often, the knowledge and age probably will be correlated.
But for other posters, I find that the language and writing style is a more obvious clue. When the two together lead to the same conclusion, I feel confident in knowing how to consider their post. In the cases of those new 'members' seeking help in the 'Disputes and Prosecutions' section, then obviously, I tend to assume that everyone is completely innocent and that the massive loss of revenue incurred by the railways every day is in no way related to their naive discovery after detection that other passengers on trains might sometimes buy tickets.
I generally assume that those posters whose interest is in liveries, class numbers and train numbers will be far, far younger than me. Always.
And then when I pass through stations such as Doncaster and notice the men in their 50's and 60's clutching notebooks at the extreme ends of the platforms, then I realise that I haven't a clue.
BTW 455driver, I will say that I'm one of the people who very much appreciate your posts on here!