I agree with Cathy! OK, it's 10 years earlier than her census ages but she wouldn't have been the first lady to have lied about her age (or gentleman either!). But if John was allegedly the same age as Elizabeth and he was 20 when they married is he likely to have married a 30 year old? Perhaps that's why she would have lied about her age.
What additional information does the marriage entry provide? Age - unlikely but you might be lucky, witnesses, parish of residence etc?
There were only two Burrows families reproducing at this time in Cranfield, John and Sarah, the parents of the Elizabeth you have discounted, who in addition to Elizabeth only baptised Robert in 1776 (a Sarah Burrows was buried at Cranfield on 2 Aug 1780); and James and Hesther (Bacchus) who married in Cranfield on 27 Oct 1784 but whose first baptism wasn't until 1789, so there's plenty of time for an earlier child. But why wouldn't they have baptised her, yet baptised later children?
There are three burials in Cranfield of an Elizabeth Burrows - 16 March 1793; 22 Sep 1798; and 13 Jan 1824 age 28, the first two of which need checking to see if there is any additional information eg dau of John
This particular batch on the IGI was taken from the transcript, which checked the PR against the BT
David