Woah, woah...easy there big shooter. Let's not talk about marriage yet

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You absolutely deserve to date a mature girl (sounds like she's the emotionally mature equivalent of a 25-26 year old) so don't let the age gap worry you. Your physical appearance doesn't mean shit to her, and you know it -
your personality does. And I would argue that anyone pursuing more schooling is trying to improve their life. That is the very definition of being successful.
Not trying to kiss your ass or anything, but I hate to see defeatist statements like that. Just go for it.