In reply to kylo-342:
This sounds very easy to me.
You've been climbing for 24 years and up to E2 before, so you're entirely competent and don't need to learn any new skills.
All you need to do is top-up your fitness with loads and loads of laps at the wall. In 6 months you can go from huffing and puffing up a 6a+ to doing laps at 6b, no problem. Once you're doing laps on 6b, then on normal rock types (i.e. stuff with holds and gear, rather than cracks or unfathomable 1-move gritstone nonsense) you can climb any E2 in the land, since you already have the trad skills.
I would do some indoor and outdoor bouldering over the winter too, as for E2 you need to be able to pull the odd sandbag 5c move every now and then, so it's useful to be regularly climbing 6a or 6b moves (so bouldering up to V3/4).
What I don't recommend is going down the wall and aimlessly doing routes around your "onsight" limit. It's pointless. It trains short bursts of difficult climbing which have nothing in common with trad. You don't need power endurance to climb E2, you need stamina. (And you certainly don't need ineffectively trained PE, which is all you get from indoor "onsighting".) You need to be able to hold on to decent holds while you faff with gear and summon up the courage to climb something that's actually quite steady, so long as you're not pumped.
Could you go climbing 3x per week? If so, you could go for a really effective plan where you focus on bouldering for a bit while keeping the stamina ticking, then focus on the stamina while keeping the bouldering ticking? The wall twice a week would do it, with a few weekend bouldering trips which are really fun anyway if you pick the right place and people.
Good luck, I reckon there's absolutely no reason you shouldn't be climbing E2/3 in 6 months (on sensible rock types) if you want to. And bear in mind that my suggestions will not help you climb grit - nothing does.