You have two main options:
1) Cancel your original auction and sell it to him outside of eBay (i.e. via email). Personally, assuming you can guarantee you'll get your money, this is what I'd do. (I'd ask for a BACS bank transfer however, not PayPal - with PayPal you'll pay fees, might have a hold put on your account before you can withdraw it (as you're 14 I doubt you'll have a credit card registered), get charged for 'accepting' the payment, and if he files a complaint about the item PayPal can take the money back off you).
2) If you want 'protection' (ha!) then end the current auction and set-up new a 'Buy It Now' on eBay for £170 for that buyer. Make sure in the description you include his user ID, the exact item you're selling and the specific terms you agreed (if any). He buys it, pays via PayPal and you're both 'protected', although it will cost you £££ in eBay + PayPal fees. Personally I wouldn't do this, PayPal and eBay are absolute jokes of companies - look after your own interests, not theirs.
I don't know why you're in a rush...he doesn't even know you've read the email yet. Don't appear too keen! And in your excitement don't forget to sort out things like delivery; insurance, time-frame, all these things add to the cost so is £170 definitely fair? If he wants it shipped to Nigeria etc., walk away.
AppleMatt