There are definitely preset triggers for many wishes, especially those having to do with skills. For example, with the fishing wishes @Mikezumi mentioned, one chain is: reach level 4ish > catch a new type of fish > catch 5 new types of fish > catch every type of fish. Catching a 1,000 kg fish is the last step in a chain that starts with a 10 or 20 kg fish, although those don't trigger as reliably, at least for me. The athletic skill has: reach level 3 or 4 > work out for 4 hours straight >> work out for 6, 8, 10, 12 hours straight, with each new one triggering about 20 in-game minutes worth of working out after the last one has been completed. Most of the self-employment careers have a reliable "make x simoleons from " chain; most of the skills that involve creating something have "create worth x simoleons" chains. The list goes on and on.
A lot of the wishes have multiple triggers though, in case you miss one. My angler sims sometimes roll the wish to catch every type of fish, for the second time, after they've hit level 10 and have already caught all types. The wish to master cooking usually rolls at level 8 plus a couple of meals cooked, but also after they "learn every recipe" (only 28, as per the original base game total), which itself triggers at or just after they hit level 9.
As for the romantic wishes, they've always been hit or miss for me. Family-oriented sims definitely tend to have more of them—if I start with an engaged couple, the FO sim will usually roll a wish to marry soon into the first romantic sequence, then to have a first child and to have a child with their new spouse within a day of getting married. Since I have them marry right away for the 2-day +50 moodlet, they get a jump on LTH points right away too.
Both of them usually get a wish to have their first woohoo with each other as soon as they exchange rings. But I almost never get that with sims I've played longer. Although that might have something to do with how... let's go with "experienced"... most of my played sims are by the time they settle down.