You sound like you're being very mature about this! Most 22yos would have stormed out in a flurry of "well its my life and you can't stop me!" leaving the parents muttering about having to pick up the pieces when the shit hits the fan 🤣🤣
It sounds like you already realise that you're not ready to get married, age gap or not. Any decent man will very happily accept an answer of" I love you, but I'm not ready to get married". If he gets stroppy, or in any way makes you feel guilty about not saying yes, then run for the hills.
Are your parents only concerned about the age gap, or do they have concerns about him as a person? With a big age gap, it often sets up a power imbalance. Some older men specifically avoid women their own age, because those women with 10/15 years more life experience than you are less easily "swept off their feet" (love-bombed) and less easy to manipulate/control in general.
I don't know your bf at all! But if anyone in your life is expressing concerns, it would be worth listening carefully to exactly what they're worried about. If they think he's a lovely guy, and that you're well suited right now, then there's not much reason to believe it's all going to go to shit as you get older (I mean, everyone changes!) But if they're brave enough to tell you that they're not so sure about him as a person, then try not to dismiss them outright.