I ride singletrack with some dudes that are 40s and 50s who can smoke me. (I'm 36.)

I would be really, really sure that you won't catch the bug and go back to MTBing. Because if you do, a hybrid is a really poor MTB... even ones with 'good' suspension forks are more like 'barely entry level' on singletrack. And the far bigger problem is tire clearance. Very few hybrids can fit even the smallest 29er tires front and rear due to not only the width but also the increased circumference.

Why am I talking about all this? Because a suspension fork hybrid is going to be within 1-3 pounds of a suspension fork 29er MTB. And the 29er can mount hybrid, cyclocross or even road tires just like the hybrid.

I wouldn't be saying these things to someone who likes to ride MUPs (Multi Use Pathways aka "bike path") and never does more than 6 foot wide gravel paths. But you loved MTBs at one time and I think there's a chance you would do it again.

If you buy a 29er and do one singletrack trail and think "nah, that's not for me" then you still have a bike that is 95% as good as a suspension fork hybrid for use on road, MUP, light trail. Go back to the Cannondale dealer and try the Trail 29er and the Trek store has no shortage of 29ers since they absorbed Gary Fisher (who invented the dang thing! ).