Well a couple things you can do, first off if there isn't any oil in the forks they will probably bottom out, second it was typical back then to use ATF as fork oil, it's even the recommended oil in the Honda service manuals. Now we have varying weight fork oils (ATF is effectively <5W). You may try using a heavier fork oil, say 15-20W, this will give you more resistive damping in the forks while maintaining the same spring rate. You can preload the forks by putting a spacer between the caps and the springs, this will stiffen the effective spring rate but the springs will bind sooner. Lastly you can look for either new replacement springs or progressive springs. I'm not absolutely sure on the 125, but there is probably 3 springs in each fork, a very short one at the bottom (the rebound spring) and 2 stacked springs with a spacer between them which provide dual rate loading. Progressive springs will replace both of those stacked springs and will compress harder the more they are compressed. Springs are sized by diameter and uncompressed length plus a rate.
On my 250s I use 15W oil, about 3/4 inch of preload (and I have adjustable caps to add more if I want) and progressive springs that are about 1/2 longer than the proper size. My setup would probably be too stiff for much jumping but then again I'm starting to drift into "old guy" territory so I'm really not looking for jumps. This setup plus a fork brace and Works Shocks spec'd for more street than dirt (custom made, you tell them how you want them... not cheap, but a bargain compared to Ohlins) on the back and the bikes have become quite sticky on the street. Before the bikes felt like they bounced around almost unrelated to the surface and felt a bit weightless over bumps, now it feels like the tires are always being shoved into the ground, like the bike is really attached and not just kind of flowing over the surface.