He backs up his claim that, past and present, he never shirks a fight by mentioning how he had killed Daeghrefn (Day-raven), whom I assume had killed Haethcyn. Although he could accomplish that without a sword, both "hand and weapon" would be needed now. Presumably, Beowulf is hinting not only that the dragon is a stronger opponent but that Beowulf himself is older than he was, and past his physical prime. He never says this directly.
The "breast adornment" that Daeghrefn fails to carry to the Frisian king may be the one that went from Wealhtheow to Hygd.
He instructs his men to stay close, but out of the fight, as he is the only one strong enough to face the dragon. He hints that he is not strong enough to survive the dragon, however: his men "can better/survive their wounds in the violent clash/than I am able."
This is still a bit rough. A couple of lines aren't properly formed, and others could be improved, but I didn't want to make you wait too long.
"I was always out in the front
"of the battle line, and always must
"be so in battle, while my blade endures,
"which, past and present, proved itself often
"since I, in the front lines felled Daeghrefn,
"killed by my hand, the Hugas' champion.
"He fetched no riches for the Frisian king
"could bring back no breast adornment,
"but that flag bearer fell with his band.
"the noble in courage. No blade killed him
"but my hard grip halted his heart's beating,
"and his bone-house broke. The blade's edge must now
"fight for the hoard, hand and weapon."
Beowulf said a solemn vow,
the last he would make. "Many trials
"I risked in my youth, and yet I wish,
"old folk defender, to find redress,
"to earn honour, if the evil one
"climbs from his cave to confront me."
He paid honour to each person,
fearless fighters, one final time,
his brothers in arms. "I would bear no sword
"no worm-killer weapon, if a way were found
"to let me go against the beast,
"grapple for glory, as with Grendel before,
"but I expect that flame will pour out in fury
"poisonous, choking, so I chose to bring
"byrnie and board. From the barrow-guard
"I will not flee a foot, but we face whatever
"befalls at the the wall, as fate determines,
"the Maker of men. My mind is bold
"so I will not boast against the war-flyer."
"Stay by the barrow, byrnie wearers,
"harnessed heroes, who can better
"survive their wounds in the violent clash
"than I am able. It is not your fight.
"No other is able. I only have the power"