Most older tractors are non-synchromesh. So, one normally selects the desired gear while stopped, and then takes off.
My parents bought their first tractor when I was 13 or so... and I don't think I had any troubles with the tranny. We plowed, disked, and harrowed, our field in the first couple of years, and I know that I got quite a bit of tractor time.
Anyway, I believe that all kids should learn to drive a stick-shift car, especially those in rural communities. The tractor stick shift isn't too different, except for the non-synchro, so no shifting on the fly.
I probably did get a pickup stuck in the ditch while learning to shift, but it wasn't the end of the world.
The hydro is nice for a lawn tractor, but I wouldn't be too worried about it for a farm tractor.
Of course, our first tractors never had ROPS, but after watching some of the YouTube videos about tractor rollovers, I'd choose a ROPS tractor, especially with kids involved.
Four wheel drive is nice. If your land is flat, you probably have mud somewhere. And, if it is on a hillside, the extra traction can be handy.