Yes. The normal requirement for RAID0 is that the two drives have the same capacity (With SSD probably best if the two SSDs are the same). "New" or "old/used" is not a factor.
Understand raid0:
.. You lose trim comand, although I understand Intel is coming out with a new driver that will suport trim when the drive is a member of raid0 conf - Only applies to Intel chipset controller, Marvel and AMD have not announced this support. The Newer SSDs do have a Better Garbage Collecter, BUT it Still Performs better with trim
.. The Biggest benifit of Raid0 is in the increase of Sequencial read and writes. Access time is unchanged and the Improvement in random 4 K is small. High Sequencial performance benifits working with LARGE file structures that are ON the SSD, even with a 240 gig SSD I don't think yo're going to stick a Bunch of 10 gig photos, or very many DVD/Bluray movies.
Both My two desktops and one laptop have daul SSDs ( Before SSDs, I ALWAYS used Raid0 on HDDs). In all three systems I chose to use one SSD as the OS + Program drive and the 2nd SSD as a "work" drive (ie placed most often used files on it).