Try this:
use master;
go
select
db.[name] as 'Database Name'
,db.crdate
,(((CAST(af. as DECIMAL(18,4)) * 8192) /1024) /1024) as 'File Size (MB)'
from sys.sysdatabases db
inner join sys.sysaltfiles af
on db.dbid = af.dbid
where [fileid] in (1) and db.crdate < dateadd(year,-3,getdate());