Ok I'm 35 and just bought my first bike a second hand carerra hellcat. I can't play rugby anymore from neck injuries so I tried road cycling and didnt like it but I know I like the woods and hiking so I was like what the hell I'll try getting a mountain bike. Thing is I went out today and though I didn't think I was unfit I got a damn shock by how badly I struggled just in my local forestry. So bad I chucked and had to walk the bike out after 4k. I literally wasn't barlet able to move the bike around in there and it was mostly gravel path and some slight trail. A lot of uphill to be fair but still, I'm feeling pretty humbled and pretty shitty. So any advice on how I can actually get into mountian biking without dieing on the bike?

Quick edit: just to say man this sub really shows up. I literally can't keep up with all the replies coming in. Thanks for all the advice I'll def keep at it I guess I was just surprised that my general level of fitness stood for nothing today on the bike. But I'll put all the advice into practice and get out there a struggle my ass off ( as is the most prominent advice haha) and persevere.

Oh and to the person whose comment I accidentally deleted, my bad, total accident.

Second edit: I'm on a damn pixel phone and I've deleted like three comments on Total accident. My bad folks I appreciate y'all taking the time to comment.