Best friend lied about his age?

so basically I've had an online best friend for over a year now and we are really close and share everything with each other, we started developing feelings for each other like 3 months ago but never got into an official relationship. we always talk about the future and how we will get married and stuff but a week ago i got to know he’s actually 3 years younger than me (i’m 21) and he lied to me. i asked him why he did that but the reason he gave didn’t really make sense. i really love this dude but my parents will never let me marry someone who’s younger than me and i’m really having a hard time trusting him now but he's acting pretty nonchalant about it. i’m very scared of losing him. (we’ve met twice irl)
what would you do if you were in my place?
Best friend lied about his age?
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