I think it will be OK. You could consider the lonesome pine trail – totally non-technical but might test fitness for a beginner.
I liked the deadwater trail – I was on a family holiday in Kielder so only had my cross bike with me, minced round the deadwater red on it and thought it looked good – wished I had the MTB. There's this loop up to the top of the fell that it pyar sh_te though. I did it in a proper rainstorm, raining stair rods, and it was just a fireroad grind up to a radio installation, then a rough fireroad back down again, which I duly got a puncture on 🙁 Well pissed off with this, but I was still smiling by the end.