Can I submit 2 years' worth of RTI data late?

[2confused2]

Hello,
We have an au pair for almost 2 years now, with a pay of £150/week, which is below the threshold for paying any taxes or NI contributions. We just discovered however that we should have registered her and submit RTI PAYE data even if we wouldn't pay anything.
Can we do that retrospectively for the last 2 years? And if so, is there a penalty for that?

Give a nanny payroll provider a call and have a chat. Yes it can be submitted and yes HMRC reserves the right to issue a fine.