I will not advise that you marry without his(dad) consent. You just need to talk with your mum since she has no problem with you marrying him.

Your mum needs to use her influence as a woman on your dad to get him to give his consent.

Also, you should have people in your family who your dad respects highly(he probably won't say No to them), just get them to talk to your dad.

Finally, try to understand his own point of view with the age difference and then you flaw his point of view.

My own candid advice is dat: just take ur time to pray over God shud touch is hrt if dat is wot u want
talk to mum, let her understand aw u feel about him. mum will speak for u for dad.

And dnt try gtn pregnant for him cos of dis... dad might not gv u his blessing. just b patience nd let G od take control