PGP keys gain trust the longer they’re used. But the likely-hood that they’ve been compromised also increases with time. I wouldn’t say they get “less secure” with time. Also, you can very easily create a new identity under the same PGP key, and revoke a previous identity. Additionally, you can certify other’s keys by signing it with your own, increasing the WOT (web of trust) with the key–asserting that the key does in fact belong to the correct person.

The keys are a bit more dynamic than you’re giving them credit for.

There’s also F/OSS which has been designed to alieviate some of the usability issues with PGP keys, mainly Keybase.