I can see your enthusiasm to suprise him, but honestly, I think he will be much happier to ride with you! I met my husband riding dirtbikes and it is one of our favorite things to do together. He loves riding and helping me and I love it when he does that too! If you really have your heart set on suprising him – firstly – I would be careful who you get to teach you ie: some other guy helping you behind his back might really backfire the suprise! Do you know any other girls who ride? I see that someone suggested that borrowing a bike at the track is easy – but I have to tell you, if some strange girl who has never riden before and I had never met before wanted to borrow my bike, I wouldn't let her and I would be a little miffed at the nerve of someone I didn;t even know asking me to borrow my expensive and breakable toy – that they could hurt themselves on and sue me for!
I am sure your boyfriend has friends who have girlfriends who ride so I would use that avenue. Hopefully one of them is the same size as you and has extra gear because you will need a helmet, boots, a chest protector, goggles, gloves knee guards and probably elbow gauds. You should have pants at least too as they really help prevent bad abrasions.
Maybe thats how you could suprise him is go and get yourself set up with gear and show him you are serious!

Yes, your bike needs to be registered and stickered to ride on public lands.

If you are taking the bike to Mexico, you will need registration, proof of insurance, your Cali Off-Road sticker, and if you'll be riding down there, I strongly recommend purchasing Mexican insurance – since your US vehicle insurance is no good there.

Best thing to do would be go to the dealerships and sit on both the 250 AND the 450…maybe some others aswell

whatever one feels most comfortable to you is best. dont get one you arent sure you cant handle because beginners luck means a lot of crashes on a dirtbike.

obviously 450 is going to have 200 more cc's then a 250 so its going to have quite a bit more power. its is also going to be alot heavier. it might sit a little to high for someone your height though?? im not sure…the last time i got on a 450 i was like 6 (riding on the back of my uncles…im now 15 but a mere 5'3…so as you can imagine something that big is of no use to me! lol). but anyways…my uncle is a big guy…like 6'2 sooo…ya.

the 250 will sit lower and be easier to handle…it will probably be a good first bike. it will have plenty of power. and dont worry about your weight being a factor…both bikes will zip around like crazy with a 200lbs dude on the back no problem.

In general these mini dirt bikes are not street legal. You should ask your local police to check out if it's legal to ride mini dirt bikes in your city.

There is some good information on riding mini dirt bikes at:

http://www.mini-chopper-tips.com/mini-dirt.html

The maintenance schedule will not be anywhere near as intense for a 2-stroke when compared to a 4. The top end will probably be the biggest hit on your wallet. Expect to do this every year or two (a lot more if you get into racing with it). People on here will say stuff to the effect like, you have to waste time measuring the oil to mix in with the gas. If you think about it, as much as you're changing the oil on your racing 4 stroke like maintenance requires, you'll be dumping every 2-3 rides almost the equivalent of what I'm mixing in. Use a good synthetic oil for whatever bike you choose (my personal favorite is klotz, but there's a lot of good stuff out there). Of the 3 bikes you listed the YZ is the best bet. Honda's CR250 is no longer in production and had weird jetting issues. The KTM SX is super light but does not have the power spread of the Yamaha or it's spot-on suspension. Is the new bike going to be used for trail or MX track? The KTM 250 XC would be a better bet if you plan on riding woods.

I would want it to be really cold because your body's temperature is already starting to escalate, so that should be able to keep you warm while you are riding so that you don't feel the cold as much.

Ok, most def a 125 is too small for you, 250cc is about what you need, If your looking for speed get a 2 stroke engine with a power band and a jetted carb. If your just looking for something to ride casually and you don't want to show-off on it, get a stock 4 stroke.

Two-stroke engines have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.

I'f your just starting out riding dirtbikes and don't know how very well DO NOT GET A 2 STROKE.
Start out with a 4 stroke or you might kill yourself, fast dirbikes are very dangerous, I know from experience.

other than that a 125 is too small for you, I have a 250 and I'm 5'8'' 155lbs.

Way more trouble than it is worth.
requires:

Modification of the charging system and connection of a battery.
Wiring of lights, head+hi-lo, brake ,tail ,marker and turn lights and all the switches that go with them including a breaker panel or fuse box.
Street legal exhaust and appropriate engine de-tuning.
Street legal tires ( Knobs are no street legal)
A key ignition.
In most states ,fender height on MX bikes are too high and need to be lowered.

And there is no "Cheating" because the bike will have to pass a physical inspection before it is licensed .

I've done a couple, A Honda XR500 and a Yamaha IT425.

Even though it's not what you want to hear ,my advice is to get a dual purpose and "trick it out" rather than trying to make a MX bike street legal.

By the statement made by you as to the other parents being liable for their childs decisions.. wouldn't that go both ways? Should you not be responsible for your sons decision to ride the bike in the first place, as well?

I think it would be difficult to prove any type of neglect on the other parents since they were not home at the time of the accident. I think you will probably have to cover this one on your own though. Unless you can talk to the other family about a 50-50 payment.

My advice would be to contact a lawyer to find out for sure.
Good Luck!

My son was about 2 1/2 when he showed intersted in anything with 2 wheels. he was riding a bicycle by 2 1/2 without training wheels and a motorcycle by the time he was 4….

make sure he can hold the bike up by himself, that is the key factor…

honestly, 2 years old is a bit young in my opinion!!! start him out on a bicycle, when he has some balance on that, and can hold a motorcycle up on his own, give him a try…

balance is the issue, but make sure to put him in all the proper safety gear!!!