In 2nd edition, it sort of depended on the setting, but generally, there was no max level. In Forgotten Realms, the max was set at 40th lvl, however. Generally, people only played up to 20th (and many people stopped before 20 and restarted a new campaign. Lots of people had a certain favorite range of levels and played through those a lot.)
I kept the Forgotten Realms standard of 40 levels, but the highest level character that naturally built from level 1 was level 13. We still play very infrequently, but it took her a good 4 years to get there. 2nd edition leveled slowly, but the power between levels might have been a bit more in 2nd.
If you're looking to convert things (and I've done this a lot... I've ran games since '95, when I was just a kid and then rode through all the editions up until now), the best way to do it is actually use the CR's of the updated monsters in Pathfinder and see how they fit. You may want to add a few or drop a few to keep the EL where you want it. You'll also want to update the treasure for your Pathfinder game, because in 2nd, a Longsword +whatever seems a lot better than what it would in Pathfinder (with all the special abilities).
In all cases though, you want your Pathfinder rules to take precedence over the 2nd edition version. Back then, in 2nd edition, hp were lower, there were fewer spells, magic items were rarer, ect. Moving forward, all these things got inflated, but then some things were softened to make up for it. Negative levels in 3rd and beyond could be taken off with a fortitude save... In 2nd, you get hit by a wight or a wraith and you immediately lost levels. No saves.... The only spell to fix it was Restoration, which was 7th level and you had to have 18 WIS in order to cast 7th level spells and be at least 14th level cleric to ever even have it. It was much different. That's a big reason why you want to look up CR's first, because some monsters became stronger and some became weaker after the d20 system... They're all AROUND the same range, but not exactly. You could even replace some monsters with something with the same flavor, but not exactly the same, just to beef up the challenge. There are a LOT of monsters in 2nd edition that were easy to kill, but would MESS you up if they even touched you. It made them scary LOL!
Anyways, the 2nd edition PHB takes characters up to 20th, just like most others in the genre. Power levels really depended on class... The classes that got the most out of leveling leveled slower than those who gained fewer benefits. In the end, it was supposed to balance it out. You can say that the levels in 2nd were equatable to the levels in Pathfinder, as long as you recognize the differences and check those CR's and EL's. All the inflation and nerfing combined kind of made it the same in later editions. When they beefed up PC hp and number of spells per day, ect., the monsters also got the same treatment. All they did was make it so that it was less likely to completely kill you off by bad luck in 2 rounds. 2nd was very gritty and 3rd and up created a buffer, while keeping essentially the same challenge.
If it were me, I would use the listed level as an actual guideline and then delve in and look at the specific encounters themselves. Most will fit the same level in Pathfinder, but you'll want to make sure one doesn't wildly swing away from the rest in power level... An easy encounter is fine, but a TPK is never fun LOL!