He'll be half a year older than Biden, but it's plausible if he thinks his chance of winning isn't too far from odds-on (the risk of reputational damage could hold him back otherwise and he'd still get to campaign against Biden/Biden's VP while rooting for a doomed Pence). I'd guess it's odds on as long as he keeps his loss to within 100 EVs of Biden, but otherwise I expect former allies to do their utmost to tear him apart. I'd also guess it's odds on if the VP-elect this time is Warren and Biden resigns in 2024.
If he keeps a high profile until the midterms (as is likely regardless of whether he runs), Trump will be blamed for any disappointments/credited with any successes there.