2 Months today since the offence. Still no word. Is this normal? I know they have up to 6 months to put it before a court but do they always need that long?
They don't always, but sometimes they do. If you look back through this forum, you'll see that quite recently one railway company(1) tried to start some prosecutions at the last minute(2). So you can't be certain that nothing will happen until the full six months have passed (plus a few weeks for the court to issue the notice).
Footnotes:
(1) Merseyrail - which isn't the company that affects you, but it does go to show that the railway companies can use the whole time they are allowed in law.
(2) And it looks as if Merseyrail actually went past the time they were allowed: if you do get told that you are being prosecuted after six months, check back here and we can go through the legal time limits with you then, to make sure that the law has been followed.