To upgrade, or not?

Yes!

If you continue to develop & refine your skills on that 125…you’ll be an excellent rider. 

stick to the 125 for another 6-12 months and then switch …. you can thank me later! 

Concentrate on maintaining momentum through the turn, getting on the throttle earlier and let that thing rip!!! If you watch any videos of pros on 125s it doesn’t look like they ever brake or let off the throttle… momentum is your friend which will negate the need for low end torque (there is none on a 125) and you will be exiting the turn in the meat of midrange and into top end and SHHIIIIFTTTT!!   

With the broad range of riding you do, upgrade to the 250x, you'll never look back!

You should definitely get a CR500

250X’s rock

taking in account your age and the doubts you refer as to your ridding technics

my advice to you is, invest a bit in yourself, do a couple of good ridding schools, get an idea of where you are at and set good targets to aim your ridding evolution.......then worry about the best bike to suit you.....now you have a great learning bike.... dirt bike ridding is always more rider then bike......

Maico 700 or take up ballet 

Best part about 125s is that if you can’t clear something on a 125, you probably shouldn’t be jumping it anyways. Stick with the 125 until you feel like you’re over riding it, not that it doesn’t have enough power. I know those seem like the same thing, but it’s a critical difference. 

I completely understand what’s going on. I have an RM125…a bit more “light switch” than your motor; but, man…when I get it right? It’s like I’ve won a Supercross. 

KTM should have the 150 kits out soon. That helped quite a bit on the carbed bike especially for woods riding.

The trade off is to maybe have a little more fun now, or use your current bike to develop a skill set that will make you a better rider for the rest of your life. A year or two on 125s will payoff in line selection, corner speed and keeping momentum skills that translate to every bike you ride in the future.

Don’t forget that a 250 smoker is lot more bike to ride, it’ll bring it’s own challenges to learn and manage. I love 250 smokers, but they can be challenging too.

Try going up 2 teeth on the rear sprocket to add a little low end. It's a lot less expensive than a new bike.

The hole I see in your argument is that you want to sell a used 125, then buy a used 250 and have money left over for a truck. Just how much do you think you're going to get for your clapped-out 125XC? (That's not a dig at your maintenance skills, just an assessment of what every buyer everywhere is going to think - they'll offer you $1500 cash for that bike. "But it's CASH!!") 

I feel like if you break even on the swap from a 125 to a 250, you will have done well.

125s are awesome to learn and refine on, I’m still riding the same 125 I was at your age and I’m 23 now. There’s no other bike that delivers the smiles that a 125 smoker does. 

i love the yz250x.  do it all, easy to ride 2stroke.  

To go from a used 125xc to a used 250xc is probably going to be over $1k. You might be able to sell the 125 xc and get an older used yz250 and break even.  

At 16 mom/dad are likely financing or paying a portion. Get that 250 before they cut you off.

I think you took the mom/dad financing part literal. Either way they are footing the bill. You might make your own money but you don't support yourself so give them the credit they deserve.