This may be tough if the space is super tight for a few reasons, but worth considering.I could talk water heaters all day...

Flipping in Mass is tough just due to the cost of entry.

You are protected up to $250 individually and $500 as a couple based on my understanding and opinion, keep the orders and the documentation that supports the timeline because you're likely to have to prove it several times but I dont think you have much to worry about. 

The burden of proof will be on you and most likely you will fail to prove that it would be arms length transaction if you decide to co-invest like this.

Called the cops, cops told us to take stuff out to the corner for the mystery tenant to take back and change the locks.We couldn't prove the agent had the only other key.

This is a tough one. 

Getting approval from the lien holders is tough enough, but if it's a regular bank they may not make it feasible to assign the contract.

At 17 and with $290, I would start planning and doing a few things: I would stick with learning as much as I could here on BP for free, maybe joining some local RE groups and get to those meetings where I could mingle with them and get known, being 17 you have youth as both an advantage and as a DISADVANTAGE till people get to know and know you as a dependable dedicated man on paper and screen till you have successes under your belt you may be looked more as a liability as you are 17 so you must prove your worth more.

The tough part about it is that I see kids that goes to private and does nothing with their lives after graduating.

You should start building relationships one by one and put effort toward not only learning from others, but doing what you can to prove your worth to others.