Once a cheater always a cheater?

Before I start I just wanna say this isn’t about a dude cheating on me, it’s about me cheating on another person. And yes I know people say there’s no excuse and stuff and I really truly understand that at the level of maturity I am now. But. At the same time. I think, for me, there IS a valid excuse- I was 13 years old. And most people were morons when they were 13. I’m pretty sure even if someone did cheat when they were 13 they wouldn’t even count it because they were so young it didn’t even count as like a real relationship. How are you gonna be 21 holding against yourself what you did when you were in middle school? Now the reason I myself do actually count this relationship as a real relationship in my dating history is because we were together for 2 years, he really was the first person I ever loved, it was the first long term relationship I’d ever had, it taught me a lot about abusive relationships, red flags, etc. So if someone asked me about my relationships, yes, I would count that as one. So that in mind, it feels wrong to count that relationship but also un-count the fact that I cheated in it? I’m a very honest person. When someone asks me if I’ve cheated it’s very difficult for me to say no. The only reason I’m even tempted to is because of blanket statements like “once a cheater always a cheater”. I get the word yes out of my mouth and sometimes people refuse to even hear me out. They don’t even listen to the circumstances. They just immediately resent me or think much less of me. I guess I’m coming here because I’m SICK of feeling guilty for something I did when I was so little. I wasn’t even ready for a relationship. I guess I just need advice. It’s really hard. I don’t want to have to say yes when a potential dating partner asks me if I’ve ever cheated, but I’m conflicted because I’m not sure I deserve to say no. I’m not saying what I did was justified, just that it in NO WAY represents who I am now and it shouldn’t be held against me. What should I do?