I started at age 51 and found a local buddy through the shop. He moved 3-4 years later and I started diving solo. Boat dives in the Southern US meant I'm at the mercy of whoever is assigned to me as a buddy. Most of the time things went fine, both in my first few years and later. I did one week in Panama by myself (wife not a diver). Was lucky in that I was the only customer on the boat 4 of the 5 dive days. Maybe two of the quite a few "instabuddies" I've had were less than desirable. These are not things you should worry about, as it is what it is. As long as you are responsible for yourself. Well, you can search on SB for all the legal ideas about buddy responsibilities, but even as a DM, I just don't let any of that bother me. It's always a good idea to check out everything that may concern you when booking a trip or a day charter. Some want to know if smoking is allowed on board. Is there a head? Do you have a good place for dry stuff? So asking about buddy policy is always a good idea if you are concerned. If there is an odd number of divers, will there be a group of three? Is the divemaster in the water---can I pay for the DM to buddy with me? Usually I just pay my $100US plus $20 DM tip and show up.
Oh, as in a recent thread on the "real world", thorough buddy checks are a rarity. Make sure you do the kind of check you want with a new buddy--dive plan, gas, weight releases, alternate air share, signals--whatever you feel comfortable with.