Some of this is not a training problem, and treating it like one wastes time your dog may not have. If they are distressed when you leave, if they growl or guard their food, their toys or you, if they are frightened on the lead, or if anything about them changes suddenly at any age, contact your vet the same day. A tip from a website, ours included, is not the answer. If it cannot wait, contact your nearest emergency vet now.
With a Springer, watch their drive. A Springer who stops wanting to search, sleeps more, puts on weight or feels the cold is telling you something: an underactive thyroid is on their record from prime adulthood. So is a Springer who shakes their head after every walk, licks their paws for hours, or starts bumping into things in the evening. Bloat (GDV, a twisted stomach) can happen in any dog, though it is most common in large, deep-chested breeds. A swollen, tight belly, retching with nothing coming up, sudden restlessness or drooling is an emergency: contact your vet now. The rest are easy to put down to age, and catching them early saves months, so tell your vet that week.
The sock drawer is theirs now. If they stop raiding it, tell your vet.