Funding your own training could well be crippling: it's roughly twice the cost of the equivalent fixed wing training. Those rotary pilots that I do know that have funded their own training from modest backgrounds have worked another career path to afford to get them training to instructor level, where they log hours until they can afford an IR. The big problem is always banking twin turbine hours. Many, or most, corporate/offshore/EMS/police type flying jobs require minimum twin turbine hours for employment, the cost of which is usually out of reach of most, as you'd be struggling to even self-fly-hire such an aircraft due to insurance requirements. The 'easiest' way to get lots of twin turbine hours is, of course, the forces.
The age thing you can look at in two different ways. Yes, you'll be on the upper limit so the RAF might not perceive this as them getting the most out of you in terms of length of service, at the end of the day you'll still be under 40 on finishing a full term commission either way. However, you could also say that if you're 23 this is their last chance, and if they want you they need to take you before you're too old.
If pilot is what you really want to do, then go for it whichever way you can. Don't accept observer in the hope of transferring, from what I've been told only once in a blue moon does this happen.
Consider offshore work as another route. You'll be bonded to pay for training, but you'll be getting all your tickets for little expenditure.
I probably haven't said anything you don't know already, but still.
EDIT: Just noticed you live in Aberdeen... probably the biggest offshore helicopter base in the UK.