Beyound the general wrongness already mentioned, let the physical impacts inform the role play.
Not just the shriveling and varicose veins, but the fact that it directly impacts one’s stamina and health.
Does your character remember when they could climb stairs without needing nap?
Do they think it unfair that, for all their power, a reasonably athletic teenager could kill them with a stick?
Are they now germaphobes, constantly in terror of a disease or infection that is only a threat to the frail? (Edit: Until/Unless they have turned themselves into the world’s most fragile statue, gratitude @Tephra ).
Do they miss the times when they were once able to perform without embarrassing themselves in bed?
Was that sacrifice worth it?
Do they hate those who are still whole?