Is there a restriction on the height or rather how low the d ring can be as I am only 4'2" so can't reach the ring to hook the pole on and my dad does not trust me enough to helm the boat yet due to my young years (all 8 of them!!)

There isn't a limit as far i can remember.

Also consider self launching poles (Pull a string and out it goes) for supersmall crews.

The beauty of self launching poles for youngsters is firstly it flies back in hopefully above their heads & secondly Dad (or Mum) can always give it that last heave on the way out.
Young crews are also better to scramble forward if they made a cods of the drop. The down side is their not old enough to buy Dad a beer afterwards by way of apoligy

Search this forum for "twin poles".  One of the links has a bunch of stuff about launchers including a link to some 505's.

My first boat had a self launching spinny pole, and it was brill great for the lazy or smaller crew. Nearly got speared a few times just tell your dad to duck faster if he complains.

Try standing on the centreboard case as well as having a lower pole ring.  This has worked when I have had vertically challenged crews.

Its not vertically challenged its being a short ass, helms need to provide proper food with good nutrition to enable better growth solving the problem

There is no restriction at all on the height of the ring.  With max length poles you lose very little from dropping the height of the pole eye, the only problem is of not drilling holes in the mast at the same height as the gooseneck, puller and lower shrouds.  If you glue the fitting to the mast (see Dan Alsop) then that's not a problem either.  Not all boats have the right sort of centrecase for the crew to stand on it to fit the pole and it's a bit precarious in a seaway, Ellie used to tell me.  I have 2 eyes on the mast now and almost always use the lower one.

P.s. Self-launching poles are fine when it all works, can be hard work for a young crew to pull out and  risk spearing one or other of helm and crew on return.  The standard twin pole system has the benefit of being well-tested and reasonably simple

I used to have self launchers on Del Boy 3365 and yes you've guessed it I got speared once. Result - One broken nose, rather alot of blood ans as for ducking I didn't even see the bl~~dy thing coming!!! Such fun?? Anyway, looking forward to seeing you all in dear old Salcombe this weekend Alleeezzzzz the Woods!!!!!!!!!!1