UKH

Forearm pump is what occurs first at the wall. What's the best home exercise to help overcome this?

Do you have a fingerboard? Certain exercises on that can help with building forearms up.

Probably not a home activity but - go climbing more 

7:3 repeaters on a hangboard, 10 sets of 6 reps. 1 min rest between sets.
 

Start with a couple of easier routes at the wall, build up slower to trying the hard stuff.

Invest in a system board. I use the Crusher set with a few extras on 18mm 2.4mx1.2m ply set at 15 degrees. I have a 300mm kick board at the bottom with good, ok and poor holds for feet. Additional foot holds higher up for training specific moves. Great way to train endurance, finger strength, specific weaknesses.  As the holds are very forgiving and you can have a long, easy session if you don't feel energetic or strong. Great for intervals, gains are rapid, easy on the skin and remarkably useful in developing footwork/core strength.

If I was doing it again I would like to be able to vary the steepness (make it steeper) but wouldn't change from 15 degrees if had to fix. I also have one side up against a wall and would prefer to have at least 1m either side to have space for flagging moves.

I took 40cm of PVC pipe, suspended a weight from it on 1m of cord, and raised the weight by winding up the cord using both hands. A couple of reps, rest, do it again.

Coupled with squeezing a rubber ring (from Decathlon)( https://decathlon.fr/p/_/R-p-313249 ) and climbing more often, I've extended my bouldering sessions from 45 mins to two hours plus before I look like Popeye.

Can't say for sure which part of the routine is most effective.

Thanks for all the suggestions. To be clear I'm old and weak I don't think a training board is for me. 

Visits to the wall are time limited because I get pumped too soon and don't think I get value for money currently.

May well try the home recommendations, the Decathlon rings and the pipe rolling.

It's really does sound like you are letting yourself get flash pumped.

Due to your long years of experience I'm loath to suggest you aren't warming up properly.

There is an art to warming that requires you to initially hold back on your effort rather than going "hasta la muerte" first or second climb...

10 sets?!? You should be climbing 9a! I've climbed 7c and can barely manage 3 sets, and that's with much longer rest times 😂

Keep to easier routes at the wall and classic trad up to severe and if you do enough the fitness will come. Quite a common problem for beginners, or in your case  after a long layoff. Fingerboard is the worst thing you can do as tendons can't yet take that kind of strain. Certain to result in injury. Fortunately I kept up with training over the years so only notice the pump on 6b/c's. We all assume that anybody else has similar fitness. Probably better to keep the weight down as this certainly helps make a difference. Developing better technique/flexibility also helps. ps. I'm 76 in a few weeks.

For an endurance set you’d either use bigger holds than the standard 20mm, or take weight off.

I would definitely start on some very basic hang board repeaters as suggested above.  Either get a hang board or just get a single large campus rung (40mm or larger so you minimize risk of finger injury) and mount that somewhere you'll use it.  Few sets a couple times a week, nothing crazy, and hang from it every other time you walk by it or something.

You're absolutely right! Over enthusiastic, and the recent cold temperatures at the wall don't help at all. I will take this on board.

As above, taking the time to do a slow, gradual warm before attempting anything near your top grade definitely helps - even more so as one gets older. Indoor sessions for me start with maybe three routes at least four grades easier than my top, and work through several at every step upwards before a few attempts at my max grade to finish. Also make sure you rest long enough between routes - climbing in a three helps, forcing you to wait longer for your turn 

I'm glad it's not just me finding that alarming

Winding towards or away from you?

Both. But not sure what difference it makes; I presumed that the muscles are activated slightly differently, and I further presumed that that's a good thing.

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My latest fitness gadget is rather like a painter's trestle to which I've screwed one of those pull-up beams. Laying on my back, I grab a different hold each time, and do a pull up with my whole body straight, from heals to neck. Works the core like billy-oh; the core gives out before the fingers do. In the climbing gym I was having the most trouble with climbing under roofs and this new exercise seems to do the trick.

As with all my other physical efforts these last couple of years, I'm reusing muscles that have been asleep almost 15 years ! It's been hard, and many on UKC have rightly observed that if you don't use it, you lose it - how right they are !