post up a pic of it showing the label or markings.
If your bottle is out of date, you can send it to H-pac for a retest. http://www.hpac.co.uk/index.htm
NPF wont test them on site although they can tell you if its out of date.. The tank will need to be sent away or taken to these guys http://www.hpac.co.uk/.
If its an aluminium cylinder then the born date is stamped into the cylinder.
It's not really viable to retest aluminium cylinders unless you can get a rock bottom test price
A fibre cylinder will originaly have the born and final dates(month/year) in the label markings.
Once retested the centre will add a test date label
HPAC are the preferred testers for paintball but dive shops can also arrange testing