The precise date of his birth cannot be determined with certainty. The chroniclers describe him as a young man (juvenis) at the battle of Stirling Bridge in 1297. The description is elastic, but probably it would not have been used at all unless it had been intended to mark the fact that his youthfulness was particularly striking. Harry is definite—doubly definite; but he is vexatiously contradictory. He is, indeed, emphatic on the point of Wallace's youth; but he gives two violently conflicting statements without supplying the means of confident decision in favour of either.
In the first place, early in his poem, Harry makes Wallace eighteen when he killed young Selby at Dundee. The date he intends is evidently about December or January 1296–97. This would make Wallace about nineteen at Stirling Bridge—an age incredible to many, though, in our opinion, not very difficult to accept. The Selby episode, however, may readily be thrown back to 1291–92, in which case Wallace would have been of the more mature age of twenty-three or twenty-four at Stirling Bridge, while still his youth would be distinctive enough for special remark. This age is accepted by the Marquess of Bute, who would place Wallace's birth in 1274; and it is an age that would still favour the Marquess's impression that Wallace's extreme youth 'was one of the reasons for the shyness with which he was undoubtedly looked upon by many of the more leading among his own countrymen.'
In the next place, however, towards the end of his poem, Harry expressly states that Wallace was said to be forty-five when he was betrayed to the English; and here he seems to rely specifically on Blair and Gray, on whose chronicle of Wallace's deeds he professes to base his poem. In xi. 1425–8, he says:
'Thir twa knew best off gud Schir Wilȝhamys deid,
Fra xvi ȝer quhill xxixty ȝeid.
xl and v off age Wallace was cauld
That tym that he was to [the] Southron sauld.'
Now, if Wallace was forty-five in 1305, he would have been born in 1260, and would have been thirty-seven at Stirling Bridge; but then he would hardly have been described as juvenis; nor does forty-five fit in with Harry's previous chronology, which ought also to agree with Blair's record. Carrick makes a desperate effort at reconciliation, by suggesting that the transcriber of Harry wrote 'forty' instead of 'thirty'; but 16 + 29 = 45 in incontrovertible arithmetic. There remains, however, this insuperable difficulty—twenty-nine years back from 1305 brings us to 1276, some ten years before the death of Alexander III.; and during this decade, as well as for at least five years later, there was profound peace, and there could have been no 'deid' of Wallace's for Blair and Gray to know.
Lax as Harry is, one hesitates to saddle him with such an egregious contradiction. If it were worth while to bring him to reasonable consistency, one might reject the forty-five couplet as an arithmetical exercise of the transcriber, with his nose on the preceding line and his mind vacant of all other considerations. Then Harry might be taken to say that Blair and Gray were intimate with Wallace from his sixteenth year till he was out twenty-nine. If he was in his thirtieth year in 1305, he would have been born in 1275. If he killed Selby in 1291–92, he would have been in his seventeenth year, which is close to Harry's statement, and at Stirling Bridge he would have been in his twenty-third year.
If we put Harry out of court as an irresponsible romancer, then we are thrown back upon the elastic epithet juvenis of the chroniclers, and the date of Wallace's birth becomes movable according to the fancy of the reader. At twenty-two or twenty-three Wallace must undoubtedly have been a man of exceptional (or at any rate impressive) physique, commanding energy of mind, and magnetic enthusiasm. More than that, he must have been at least as experienced a soldier as any Scot in the army on the slope of Abbey Craig. There must be an accentuated meaning in the epithet juvenis. In fact there need be little hesitation in reconciling Harry with the chroniclers and with himself. Wallace may be taken to have been born in 1274 or 1275.
Wallace had certainly one brother, Malcolm, who was older than himself; possibly another brother, John; and perhaps two sisters. It is recorded in an extant letter, written on August 20, 1299, that at the meeting of Scots barons at Peebles on the previous day, Sir Malcolm Wallace and Sir David de Graham drew their knives on each other over a demand of the latter for the lands of Sir William Wallace, who was going out of the kingdom without leave. The accuracy of the writer almost conclusively bars the supposition that he could have blundered on the name Malcolm instead of John, as has been suggested. If this be so, it supports Wyntoun's statement that the 'elder brother enjoyed the heritage,' and negatives Harry's assertion that young Sir Malcolm was killed, with his father, at Loudon Hill in 1296—or rather in 1291. Bower mistakenly calls him Sir Andrew.
A Sir John Wallace was undoubtedly executed in London in 1307. The sanctimonious Langtoft gloats over the details of the execution, and says his head was 'raised with shouts near the head of his brother, William the Wicked,' on London Bridge. It has been doubted, on no very clear grounds, whether Sir John did not belong to the family of Riccarton. Harry mentions that Wallace, during his Guardianship, 'his brother's son put to his heritage'; but this is on the presupposition that Malcolm was slain at Loudon Hill; and Sir John could hardly have been young Sir Malcolm's son. Even Langtoft may for once be right.
For the sisters there is only the authority of Harry. He mentions Edward Little as Wallace's 'sister's son,' and Tom Halliday as 'sib sister's son to good Wallace.' If Harry be correct, these sisters must have been much older than Wallace.