I'll echo what Steve and Phyl have said: age is no longer considered a factor by doctors who treat with radiation. Statistics show the trend is increasingly toward treating ANs with radiation, due to the comparable results, shorter recovery period and virtually non-invasive nature of radiation. A recent survey of neurosurgeons revealed the majority would personally choose radiosurgery if they had an AN themselves.
All that said, there are many reasons to have surgery instead of radiation, large size and close proximity to the brainstem being a couple, and personal preference (some people don't want a dead tumor in their head; they just want it out) being another.
Like you, I was nervous about having my vestibular nerve cut on my AN side. Although many people compensate for the loss, I'd heard some anecdotal stories of people who didn't and suffered chronic vertigo afterwards. My problem with cutting the vestibular nerve is there is no guaranteed outcome and you can't go back once it's done. Of course, the same can be said about radiation, and the longterm effects are what worry some doctors enough (including Dr. Brackmann) to recommend against it for young people. You just need to choose your poison.
As far as I know, there are no verified cases of malignancy resulting from radiosurgery (GammaKnife, or GK) or radiotherapy (CyberKnife or CK, and standard fractionated stereotactical radiosurgery or FSR). GK has been practiced for over 40 years in the US. You will be 87 forty years from now. CK is very similar to GK (the main differences being CK offers a slightly better chance of hearing preservation, splits treatment into multiple doses, is totally non-invasive, and delivers a more homogeneous dose of radiation throughout the tumor).
I recommend you get at least three opinions before choosing which treatment to have: one from a surgeon (which you've already had), one from a CK practitioner, and one from a GK practitioner. Also consider getting an opinion from a doctor treating with standard FSR (FSR is considered to be a little less accurate than CK and GK, but many forum members have had outstanding results with it). The only way to form a really valid opinion for yourself is to get these multiple perspectives (along with their attendant biases) from doctors who use different approaches. By the time you hear from all the professionals, you will have a gut feeling which treatment is best for you.