If aluminium then that is genuine, there is what appears to be contradictory information for simplicity about with it sometimes being referred to as 5 years, and you may also find cylinders marked by the manufacturer as needing testing at 5 years but only legally requiring it at the 10 year point.
Eg the law page on ukpsf.com shows the full details with 3,5 or 10 years depending on cylinder type / design, but the hpa1 handout showing 5 years.
Sites may not allow aluminium cylinders past 5 years even if they are valid to 10, but you can print & laminate copy of the law page to show them.
What you need to be sure of is the cylinder type and if aluminium it will be marked with a code to identify the alloy type as aluminium
Both aluminium & steel cylinders are genericaly called steelies, but a true steel cylinder will be a rare sight
(Note the 3 year cylinders will either no longer be around or will have been retested up to a 5 year sequence)
http://ukpsf.com/paintball-and-the-law/
http://ukpsf.com/wp-content/uploads/2013/03/hpa.pdf
