I admit I've always been a social and friendly person. My spouse and I have traveled and I almost always during the trip end up befriending someone and getting a way to stay in contact, with many I even end up visiting in subsequent trips that pass through the same area.

But for friends from before my 30s and even before my 20s? That is different. Most of my closest friends we've scattered across the planet in our travels and lifestyles, so it is less in person there. Writing letters, sending messages, gifts, postcards, the like is how we do it.

My biggest suggestion is to find a hobby and use that to build a bridge.