Sorry I came in late to this...
Your goal is going to be SLOW progression without injury
Start off with joint mobility, slow. Older muscles NEED to be warmed up well. If you try to do something like Seb Foucan's warmup, start slow, and increase speed gradually.
Barefoot/ VFF walking is a start, but if he's not used to BF, keep it short.
Balance is a good skill - low impact. Start with standing balances, and low level moving balances. Walking curbs, railroad rails, stepping from rock to rock...
Depending on your dad's enthusiasm, he may NOT know when to stop. It's actually pretty common, especially if he used to be in pretty good shape but hasn't done anything in a while.
Walking, running, QM [crawling], climbing up & down easy things, small jumping [in place to get landing down, then small precisions and drops, then build to safety vaults] ...
Impact is going to be the hardest thing. Running and jumping. Just watch closely, and try to keep him from hurting himself
