It refers to when you feel a different age than you are. When told your real age it produces a profound state of dissatisfaction and/or unease. Prolonged effects of age dysphoria may derive into depression and/or anxiety.

Said dysphoria does not necessarily see itself linked with sexual desire towards any specific age group, or gender. Although the term has been adopted before by paedophilic individuals to justify their attraction to children, which has given it a questionable reputation.
Stop telling me im 20 years old, it's giving me age dysphoria
by Ledditor September 29, 2021
Get the Age dysphoria mug.