Girlfriend lied about her age

Today I found out that the girl I've been in a relationship with for 9 months lied about her age by one year (actually 18 instead of 19) to me (22). This really shocked me when I was at work and I spent all day thinking about it with an unwell feeling in my stomach.

Our relationship so far has been good. We usually settle fights quickly, I do notice her not assessing things rationally sometimes however those are never major topics. She supports me in tough times and always proceeds to learn more about how we can improve as partners.

When we started our relationship we did talk about age as I already felt unsure about dating an (what I thought at that time) 18 year old, as a then 21 year old. I had made my concerns clear and we decided to give it a try. This was also what scared her from revealing the truth as she really wanted our relationship to work out and she's been showing me all her love ever since.

Now. I've posted about this on two subreddits. While one subreddit, people seemed to be quite unified in having a strong opinion against our relationship I was quite surprised and confused when I also asked a German subreddit (as we both are German) and most seemed to make no big deal out of it. The difference was day and night: basically, "break up immediately, huge breach of trust" vs. "you're both kids, it's no biggie and that's a typical mistake for a 17 yo that you'll be laughing about in the future".

All of this has been tearing me apart. I don't understand how I can get some more clarity. My mind is split just as much as the opinions that I hear, so those didn't really help. Should I make this a big deal? As I'm not a native English speaker, feel free to ask away if you have any questions understanding my text.