NYM
The normal rule is after 5 years 'out' you're treated as a new joiner but depending on branch and trade there are possible waivers to be had on various bits of the entry standards and training requirement.
Current plan has 609 Sqn at Leeming in the RAF Regt role and what the medical branch really want are paramedics and nurses rather than the old 'medic' trade. There are other opportunities likely to arise from the restructuring of the Reserves if you're prepared to give another trade a go.
For now why not register an interest with 609 Sqn and then the recruiters will advise further.