At what age should hens begin to lay?

Wow, a double yoker - that's great.  I got my hens in November and they only started laying towards the end of February at the age of approx 30 weeks.  They don't lay every day but most days.  I have heard others mention that they sometimes lay the odd one or two and then take a bit of time before they settle into laying regularly.  What breed are they?  I'm sure you'll find they will start to lay regularly soon and also if one starts then the others follow suite fairly soon afterwards.

first of all check that they aren't laying elsewhere (one of mine was laying underneath a tarpaulin on the back of a lorry (she had a lovely big pile of eggs when we discovered them), but otherwise don't worry they will settle down and amber stars are very good layers (don't wish for too many double yolkers though as they aren't good for the hen  )