Tendency for youngest being vacuous is reversed after 2 perhaps (10)

'tendency' is the definition.
(I know that propensity is a type of tendency)

'for youngest being vacuous is reversed after 2 perhaps' is the wordplay.
'for' becomes 'pro' (as in being 'pro' something).
'being vacuous' says to hollow out the word (remove centre letters).
'reversed' says the letters should be written backwards.
'after' says to put letters next to each other.
'e perhaps' becomes 'pen' (I can't explain this - if you can you should believe this answer much more).
'youngest' with its centre taken out is 'yt'.
'yt'+'is'='ytis'
'ytis' backwards is 'sity'.
'sity' after 'pen' is 'pensity'.
'pro'+'pensity'='PROPENSITY'

Can you help me to learn more?