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 alleviate some of the usability issues with PGP keys, mainly Keybase.