Using 'untalented' can sound harsh or critical. Use it carefully to express lack of skill without offending. He finds painting difficult and considers himself untalented.
Pro Tip 2/3
Context Matters
'Untalented' should be used in contexts where skill levels are being assessed or discussed. The director searched for promising actors, but many were untalented.
Pro Tip 3/3
Subjectivity
Remember that 'untalented' can be subjective. One person's opinion might differ from another's. Some say he's an untalented writer, but others enjoy his unique style.