I had an old Aleeda wetsuit from 1990 - started doing triathlons again in 2002 after a 10 year hiatus - wore my old suit - it worked pretty well. Decided to buy a brand new - super flexible - top of the line fullsuit. Its not any faster.
Disclaimer - my old suit was sleeveless (actually it had short lycra sleeves) so flexibilty was not an issue.
Go for some swims - if it seems o.k. - its fine.
Dave