Retaining rank usually depends on what regiment you're joining and how long you've been out. For instance, non armoured guys joining us have kept their rank but on the condition they passed the necessary trade courses within an agreed time scale. This may vary from unit to unit and is almost certainly also subject to the CO's discretion.
Depending on where you're at after your 24 years, there is also the question of availability of a slot to match your rank.
If you are still in then speak to your RCMO and get the significant bonus on offer for transferring.
There is a recent DIN out which explains everything. Go and see your local TA unit and ask them about it. Don't be fobbed off with 'at CO's discretion' comments - get them to pull the DIN off the system- it's all in black and white.