I'm 1 month away from a trip to Nepal, I still have time to chop and change my itinerary, but until a few days ago I was looking at Gokyo Lakes/Ri (not including EBC).
This weekend I did Ben Nevis via the Pony Track, the toughest thing I've ever done in my life, by the half way point (just before the zigzags start at the small burn) I was knackered and the walk up the zigzags pushed me past my limit.
So, knowing that, is Gokyo Lakes aiming too high? what would you suggest instead? I was thinking that perhaps Annapurna Base Camp might be easier, but I'm not sure?
Agree with Mike - plenty of time to get fitter; concentrate on aerobic stuff rather than endurance (you'll have enough of that on the trek).
Consider the Jiri/Shivalaya walk-in - potentially a couple of hard days but it will help with fitness for the higher parts.
Use a porter or, preferably, a guide/porter.
Go at your own pace (no need to race for lodges in February)and acclimatise; ensure you have buffer days for adverse weather and flight delays out of Lukla.
If it's too much then turnback; you will stil have an amazing experience.
ABC is easier but the above still applies.
Also have a look at trekinfo.com and listen to escher and yakshaver; and the forums at lonelyplanet - take note of the info from petrus, tomtraveller and into-thin-air.
I'd go for Gokyo. If you follow a standard-type schedule you won't be able to walk that far in any one day as otherwise you'll have gone too high. On the way up we'd finished walking no later than lunchtime and on a few days much earlier. (We started between 7 and 8 and usually had a 20-30 minute coffee break mid-morning. Quite a few photo stops too, but no other big rest stops.)
Whilst some steep sections were quite hard work when we were doing them, we soon recovered and never felt worn out at the end of the day's walk. Admitedly I do a moderate amount of exercise but the other half had done next-to-nothing in the preceeding six months. Also, we carried our own gear but our bags only weighed about 10kg.
I got back from EBC a few days ago. I'm a reasonably fit walker but found it very hard purely because of the altitude- which affects most people to some degree.
Within a few weeks of starting to train you'll be plenty fit enough in my view, you can't walk that far / climb that high each day because of the altitude gain.
I enjoyed the trek so much that I fancy returning to do the Gokyo route next year or two . We carried our own packs too.
I say go for it. If you get as far as Namche and decide you don't want to continue to Gokyo you can still do several short treks from there and get some outstanding views.
I would take on board MFD's advice - get fitter and you will enjoy your trek more! Having said that if you have the willpower to keep going you will have a great time, but if you get as far as Gokyo Lake you must climb Gokyo Ri, which you may find as relentless as the Ben depending on your conditioning. Take your time no matter your fitness level - some very fit people suffered from ams on a recent trek I did around the high passes of Everest
OK... so it took you 10 hours on the Ben... and it was the toughest thing you ever did in your life.
One way of measuring how fit you are (or aren't) is to do the same thing again and again. With a bit of luck, it would only take 9 hours and be the second toughest thing you ever did in your life. Keep it up, and it will eventually feel like a walk in the park... sort of!
Of course, if you don't live in Fort William, or if you can't get there easily, then you'll have to look for other challenging walks to get fit.
As you still have a month to go, you should try to get fitter, as usually helps make it easier. You want to be training for Aerobic, (endurance/stamina), type fitness, not strength type. You also want to be getting your body used to carring weight for a few days at a time.
Hit the hills ,(if possible), with a weighted rucsack, and do as often as you can, 5-6 days a week if possible! Climbing the stairs in multi-story buildings is also a good work out! I have 3, 14 story tower blocks near where I live and try to do them around twice a week, more if training for a trip. When "younger" used to run up and down them!