Politeness levels online?
I've started talking to some Koreans online with a language exchange app and I've noticed that they don't always speak in 존댓말 even though we're strangers. They've all be 3 to 6 years older than me, so I can't get too offended, but I've read that similarly aged adults usually speak in 존댓말 until they get close. Are they being less respectful because I don't speak much Korean or because they're older or because the rules are less strict online? Should I be a little offended?
Notably, a lot of them use 나, even though they use more 존댓말 than 반말 otherwise. They use 당신 too, but I assume this is just an online thing to make it easier to talk.

Question

Politeness levels online?
I've started talking to some Koreans online with a language exchange app and I've noticed that they don't always speak in 존댓말 even though we're strangers. They've all be 3 to 6 years older than me, so I can't get too offended, but I've read that similarly aged adults usually speak in 존댓말 until they get close. Are they being less respectful because I don't speak much Korean or because they're older or because the rules are less strict online? Should I be a little offended? 
Notably, a lot of them use 나, even though they use more 존댓말 than 반말 otherwise. They use 당신 too, but I assume this is just an online thing to make it easier to talk.

Answer

I would say its nothing to do witb disrespect nor age difference.
we often use 반말 in many crowd websites and no one judges for not using formal language
I assume it happens in any country specially online talking to some random people.