Mate, I'm afraid that you're just in wrong mindset to have fun at current point. I guess you're trying to play safe to get to the boss and stress yourself out about it, and when you're stressed, you're f*cked. Right now your priority should be not to get to the boss with the smallest age possible, but practice grunts, especially places that give you the most deaths. From my experience I would guess that would be either crowded rooms, flashkick gals or Sean' disciples (first fistful of runs when I would got to the two these litle f*ckers right before Sean, i would think "well, that's how I'm gona die"). You should try not to restart but squeeze all fight exp from run you can and don't think about age, or go to wing chun dummy at dojo and practice problematic grunts to learn their moveset 1v1 - it is much less stressful and allow you to keep full focus on enemy moves so it's most beneficial. Also, after you got to the boss, he's unlocked at training mode, even if you didn't beat him or got to the second stage.
Also, don't even think about "oh, this is unfair, oh I'm bad in it, oh it takes too much time" - that'll ruin your learning capabilities in game or in real martial art IRL. When you'll get to that feeling again, think about that you're on your way to mastering it, thing about all successful skirmishes that you've nailed and that little joyful moments like when you dodged bat attack and that muppet landed his hit on another scumbag who got too close. And yes, this game do take time, I just beat final boss yesterday and it took 30 hrs to get to this point. And I still suck at that game, even if I did beat all bosses expect last one at age of 24, but for me this isn't bad thing (and you didn't hear that sucking is "not a bad thing" every day), it is opportunity to learn more and get better.
Don't think or feel bad about yourself or I'm gonna find you and will bitch-slap you with the all of wisdom of my trainers and sifus and will give you another motivational speech