Interesting strategy from your Dad when he offered to front the trials bike in exchange for you giving up road racing. That is brilliant! Maybe I try something like that...
I think you have a good goal and it certainly is achievable. You are the perfect age to try too. You have a good background to be quite successful.
I have an older son than the rider pictured above. He was a pro road racer too. He's been retired since 2008 and well along on a successful business career; yet like you he badly missed the competition. He's been casting about for hobby racing of some sort.
Last December he decided to race the Mexican 1000 this month, so he started working out and building fitness. A few weeks ago he bought a new KTM for the race. He ran his first enduro after two weekends of practice. It was a struggle, but he had a respectable finish. Then he ran a HS after that, and will run the Pine Barrons 300 next weekend to polish his navigation skills. The following week he tows to Mexicali to try his hand at a new sport.
He's a long ways from being skillful, but that is what attracts him. He gets to enjoy the learning curve just like he did in his early days of road racing. Plus, it's affordable!
Good luck and say thanks to your Dad for me. I can work with that!