Are there any hotels in Boston that let 18 year olds make reservations?

I need to go to Boston to take placement exams for the college I'll be attending, and I was wondering if there's any hotels that let you make reservations if you're 18. I've e-mailed a few (Doubletree Guest Suites Boston lets you, but there's no T stop near it), but so far, I'm not having any luck. I'm waiting on a response from Club Quarters Boston about their minimum age. Anyways, are there any other hotels that will let me make reservations if I'm 18 (Brookline or Cambridge is ok, too)? There won't be anyone else with me - no parents/friends, and I do have a credit card. The hotels would need to be accessible by the T (I'd be coming into South Station on Greyhound and taking the Green Line to the MFA stop the next day, but I'm familiar enough with the T to get around) because I won't have a car or anything. Thanks! :)
I've found Doubletree Guest Suites Boston that'll let me, but I'm using that as a last resort since I'd have to take a cab from South Station to the hotel. If anyone knows of any other places, I'd love to know!

i think there would be at least one

I never had this problem, don't ask and just make the reservation on line. They are probably being cautious because it is graduation time and prom season. There is a Holiday Inn over near Children's Hospital within walking distance to the MFA, you could try that.

If you have a credit card you can reserve at just about any hotel. You need not tell your age so do not.

As for the Doubletree: are you referring to the Doubletree in Allston near Harvard business school?? If so you can take the subway from the Airport (Silver Line connection to Red Line) to Cambridge Central Square station and then the #64 bus to as close to the Doubletree (one long block) as you can get (actually, I would assume the Doubletree would pick you up at the Subway Station - check it out).