Anne ELEY DENNYS (St. John) - Parentage looks suspect from dates

Anne Eley Dennys is recorded as having a date of birth in 1518 with her 2 children born in 1544 and 1550.

Her mother Anne St John (Neville) Ann Neville however was supposedly born in 1505 making her only 13 at the time of her daughter's birth. Possible, obviously.

However Anne senior's next children were born in 1528, 1530 and 1532 with her marriage to John St John (1494) Sir John St. John, Kt. supposedly not until 1533.

Anne senior's own parents are recorded as being born in 1484, so she could not have been born so much earlier than 1505.

I suppose a birth date such as 1502, making her born when her parents were 18 and giving birth herself at 16 would make it a touch more likely that the lineage is correct. But still...

Is it possible however that this Anne is the daughter of her father's first wife Margaret Waldegrave Margaret St. John who was born in 1485 - John St John and Margaret Waldegrave were married in 1515 before Anne's birth in 1518.