While i think there are some merits to this, there are some downsides also.
I get your point regarding togging out at Jnr B and some lad just out of minor is scurrying about the place, but are you robbing from Peter (Jnr B) to pay Paul?
Or would you say it would be more aimed at lads who have recently given up the ghost, but could be lured out of retirement on the premise of not having to run after the energizer bunny.
I also have mixed feelings about 35 year old's these days compared to yesteryear. You could argue that the advancement in fitness, nutrition and recovery means that lads at 35 are fitter and healthier than in days gone by therefore able to continue their playing days a bit longer...The other side of that coin is that, if they have played at a decent level, they will have been flogged for 15 years and be in bits.
Overall, i think its worth a pilot for a year or two. With a little support and a trophy to aim for, no reason a couple of say 10 team leagues (maybe north and south) couldn't be run, perhaps with a grand final at the end. (roll on next year )