Your proof of relationship is going to be the same whatever route you take. The only difference is that you'll have a marriage certificate to add.
Make the choice that best suits you both.
You'll not be approved quickly so you'll have plenty of time to gather more proof of a relationship too.
Take pictures! Even if you're just hanging out at home. It's still time together that can be proved.
I met my now husband only 2 times before we applied (a total of 20 days physically together) and by the time I had the embassy interview we'd met 3 times.
My proof of relationship consisted of pictures of the 3 visits together, pictures of birthday/christmas cards, call logs showing that we spoke every day, message and video call screen shots and social media posts, (to show that others knew of our relationship)- you don't need physical interaction with friends and family as any proof of a relationship. And that was it. Approved.
Your age gap is no one's business, you're both conseting adults.