Last I heard, we are short of recruits but not short of pilot recruits. Retention of experienced aircrew is more the issue.
From your latest post you imply you have previous rotary experience with the Aussie Army. I suspect that was why your mate was allowed to transfer in his 40s. However, with respect, I doubt whether your 1000 hrs on the GX will be all that attractive to the RAF although your glass cockpit experience would help. Operational experience of piloting other ISTAR types is probably of more relevance.
By all means go for it. However, I suspect you'd be as likely to end up on rotary or another multi engined type than Sentinel.
Whatever you decide, good luck.